Gemara

40a (Rava bar Shmuel): The Botze'a (one who cuts) may not [bless ha'Motzi and] cut until there is salt or Liftan (an accompaniment for the bread) in front of everyone at the meal.

Rava bar Shmuel went to the Reish Galusa's house. He blessed immediately (without waiting for them to bring salt or Liftan).

Those present: Did you retract?!

Rava: No. There is no need here for Bashash (to wait; alternatively, Liftan.)

55a - Question: "Ha'Mizbe'ach Etz... Zeh ha'Shulchan Asher Lifnei Hash-m" -- first it calls it Mizbe'ach, and then it calls it Shulchan (table)!

Answer (R. Yochanan and R. Elazar): When the Mikdash stands, the Mizbe'ach atones for the sins of Bnei Yisrael. After the Churban, [hospitality done on] one's table atones.

Rishonim

Rambam (Hilchos Berachos 7:3): The Botze'a may not cut until they bring salt or Liftan in front of everyone, unless they intended to eat bland bread.

Hagahos Maimoniyos (1): My Rebbi (Maharam me'Rotenburg) says that if the bread is spiced or salted, like our bread, it does not need Bashash, like Rava said, according to R. Chananel and the Aruch.

Rosh (6:22): Some explain that Bashash is a delay until they bring Liftan. Some explain that he said 'this bread does not need Liftan.'

Mordechai (130): Bnei Ashkenazi do not normally put salt or Liftan on the table, for our bread is dear and salted.

Tosfos (40a DH Havei): Our custom is not to bring on the table salt or Liftan, because our bread is important, like the bread in the Reish Galusa's house. However, R. Menachem was meticulous to bring salt, like it says in the Medrash that when Yisre'elim sit at the table waiting for each other to wash, they lack Mitzvos and the Satan prosecutes. The covenant of salt protects them.

Magen Avraham (OC 167:14): It is better to speak Divrei Torah than to be idle. Better than both of these is not to interrupt at all (between Netilas Yadayim and ha'Motzi).

Sefer Chasidim (102): One may not kill a louse on the table on which we eat, because it is [like] the Mizbe'ach. This is why we cover the knives at the time of Birkas ha'Mazon, for it says "Ki Charbecha Henafta Aleha va'Techalelah."

Kaf ha'Chayim (167:41): It is best to remove the knife from the table for the entire meal, except when needed. One should not kill also fleas and similar things on the table. The same applies to a table on which one learns.

Poskim

Shulchan Aruch (OC 167:5): One may not cut the bread until they bring in front of him salt or Liftan for the slice of ha'Motzi.

Taz (5): The Rambam said 'one may not cut until they bring in front of everyone.' Why did the Tur and Shulchan Aruch say 'in front of him? The Tur discusses an individual who eats, and the Gemara and Rambam discuss many who eat. They wrote 'the Botze'a may not cut...', to teach that one of them cuts. The Tur wrote only 'one may not cut.'

Kaf ha'Chayim (35): A Hagahah on the Tur says that in the days of the Gemara, everyone had a small table in front of him. Nowadays, all eat at one table, so it suffices to bring in front of the Botze'a. I say that nowadays, our bread has salt, so we need salt only to dip the slice of ha'Motzi (see 37, at the end of this Halachah), even the Taz and Magen Avraham agree that it suffices to bring in front of the Botze'a.

Mishnah Berurah (25): If one blessed before they brought salt, he must wait a little before eating until they bring salt.

Kaf ha'Chayim (36): They should bring the salt before Netilas Yadayim, to avoid a Hefsek between washing and ha'Motzi.

Shulchan Aruch (ibid.): If it is clean bread, or spiced with spices or salt, like our bread, or he intended to eat bland bread, he need not wait.

Beis Yosef (DH v'Lo): Rashi explains that Rava did not wait for Liftan because the bread was clean. Shibolei ha'Leket says that the Ge'onim explained that the custom is to cut the bread on salt because the table is called Mizbe'ach, and it says "Al Kol Korbancha Takriv Melach."

Beis Yosef (DH veha'Rambam): It seems that the Rambam explains like the Aruch, that anything eaten with bread is called Liftan. Rava said that the bread does not need Liftan, for he intends to eat it without Liftan. The Tur is difficult. He says "and so wrote R. Chananel and the Rambam." If he refers to not cutting until they bring salt, the Gemara explicitly says so! (Why does he attribute this to R. Chananel and the Rambam?) If he refers to the law that clean bread does not need salt or Liftan, the Rambam did not say so. He says that Rava did not wait because he intended to eat bland bread!

Bach (6): Rashi explains that Rava said that one need not delay for salt or Liftan, for this bread is clean. If it were not clean, even if he did not want salt or Liftan, he could not cut until they were brought. This is unlike the Aruch, who says that Rava spoke about himself, i.e. I do not need Liftan, which Chachamim call Bashash. 'One may not cut until they bring in front of him salt or an Liftan' applies only to one who needs salt or Liftan, for he is not satisfied with it without them

Bach (7): The Tur understood the Rambam to say like Rashi, that he need not wait for salt or Liftan only if the bread is so clean and dear that they intended to eat it without salt or Liftan. If it is not clean, and even so they intended to eat it without salt or Liftan, Batlah Daitan Etzel Kol Adam (we ignore their opinion. The Halachah is based on normal people.) One may not cut until salt or Liftan are brought. The Tur did not fathom that anyone would explain that one may intend to eat unclean bread bland, and cut it without salt or Liftan. However, the Beis Yosef is correct. The Rambam holds like the Aruch, that it depends on his intent. If he wants to eat bland bread, even if it is not clean, he may cut without salt or Liftan.

Gra (DH v'Chasav Hagahos): R. Chananel and the Aruch hold that one must bring Liftan first, lest he need to interrupt between ha'Motzi and eating. This is why the Rambam says that if he will eat bland bread, he need not bring Liftan. We can resolve the Rambam also according to Rashi.

Damesek Eliezer: We need not say that there is any argument between the Aruch, the Rambam and Rashi. The Rambam could explain the Gemara like Rashi, that because the bread was clean he wanted to eat it without Liftan.

Bach (DH v'Ika): The Mechaber seems to be inconsistent! He says 'if it is clean bread... or he intended to eat bland bread, he need not wait.' The Rambam is lenient about one who intended to eat bland bread, even if it is not clean. We do not say Batlah Daito Etzel Kol Adam. All the more so he is lenient about clean bread, which everyone eats without salt or Liftan. However, Rashi and the other Meforshim permit only if it is clean. If not, one must bring salt or Liftan, even if he intends to eat bland bread. If the Mechaber rules like the Rambam, he should have cited the Rambam, without need to discuss clean bread, for this is obvious. A Kal va'Chomer from bland bread teaches this! I answer that he rules like the Rambam. He teaches that whether it is clean and he intends to eat it with salt or Liftan, or whether it is not clean and he intends to eat it without salt or Liftan, for these two cases are equal, he need not wait.

Taz (6): The Rosh said that some explain that Bashash is a delay until they bring Liftan, and some say that Rava said 'this bread does not need Liftan.' Usually, the Rosh brings Perushim only if there is a difference relevant to the Halachah. The first Perush equates all bread. All require Liftan, but one need not wait for them to bring it. We say that first they must bring Liftan when it is ready, and it needs only to be brought. If there will be a delay (to prepare it), like in the case with Rava, one need not wait for this. Rava taught that one need not wait (a long time) due to this law. The second Perush distinguishes different kinds of bread. Clean bread does not require Liftan even if Liftan is in front of him. The Tur holds like the latter Perush. The Rambam connotes like it. He distinguishes - if they intend to eat bland bread, there is no need for Liftan. This is unlike the first Perush. Each of them gave an exception. The Rambam taught that if the bread is dear, and he will eat it alone, it does not need Liftan. The Tur teaches about clean bread. The Shulchan Aruch rules like both of them,

Magen Avraham (11): If many are reclining to eat, one must wait until they bring in front of every one.

Magen Avraham (12): Whenever one need not wait, he may wait if he wants. Or, perhaps he may not interrupt (Darchei Moshe). Based on Sa'if 6, that even something not needed for ha'Motzi is not a Hefsek between the Berachah and eating, even l'Chatchilah he may interrupt. This is why he was Stam in the Shulchan Aruch.

Kaf ha'Chayim (39): I.e. the Rema was Stam (did not comment), for he agrees that one need not wait for salt or Liftan (but he may, if he wants, even if it is not necessary). He retracted from what he wrote in Darchei Moshe (that perhaps one may not wait).

Mishnah Berurah (27): The salt or Liftan is to honor the Berachah and to avoid a Hefsek to request salt. It is better to wait before saying ha'Motzi. An example of clean bread is wheat bread.

Sha'ar ha'Tziyon (23): If someone cannot eat clean bread without Liftan, Batlah Daito Etzel Kol Adam (Darchei Moshe 5, citing Or Zaru'a 1:141).

Note: Seemingly, if he needs Liftan, he should bring it before ha'Motzi to avoid a Hefsek afterwards! Perhaps this is true for one who blesses for himself. The Or Zaru'a teaches that the Botze'a need not wait even if one of the others cannot eat it without Liftan. His initial words discuss waiting until Liftan is brought in front of everyone.

Rema: In any case it is a Mitzvah to bring salt on every table before slicing, because the table resembles the Mizbe'ach, and eating is like a Korban, and it says "Al Kol Korbancha Takriv Melach." This protects from punishments.

Magen Avraham (15): Even though our custom is not to eat salt, because there is salt in the bread, it is a Mitzvah to have salt on the table.

Kaf ha'Chayim (40): It is the woman's Mitzvah to bring salt. Lot's wife became a pillar of salt because she did not want to bring salt to the table.

Mishnah Berurah (31): Eating to strengthen oneself for Avodas Hash-m (is like a Korban).

Mishnah Berurah (33): Mekubalim say to dip the slice of ha'Motzi in salt three times.

Kaf ha'Chayim (37): Bread and salt (Lechem and Melach) are composed of the same letters. Their Gematriya is 78, three times that of Hash-m's name. Dipping three times 'sweetens' three Gevuros (harsh judgments) in salt through the Chesed in bread, and expels the Satan. Some dip the bread in sugar at a wedding or on Rosh Hashanah, for a good Siman. This should be done after dipping it in salt.