I noticed that among Orthodox and, seemingly Hareidi Bar Mitzvah's and weddings, a huge challah is cut by the chattan or Bar Mitzvah.
I assume that there must be some minhag behind this that originated somewhere for some reason. I don't think it's just to feed the attendants, because usually bread or rolls is available in a table bread basket or at each seating, and the challah is usually cut (esp. at weddings) long after people ate the appetizer / first course.
The earliest source for having a large Challah at a wedding is the Maasas Binyomin (d. 1620)
There is a wide spread custom to distribute slices of the large challa to the friends of the Chosson and Kallah. Some say (Nittei Gavriel quotes Darkei Chaim p27, who heard this from R' Akiva Eiger) that this is based on the famous question posed at every marriage: 'מצא או מוציא' - every marriage has the potential to be ׳מצא אשה מצא טוב׳, or conversely to be 'מוצא אני את האשה'. Therefore immediately after they partake of it, we remove the ׳המוצא׳ from in front of them, as if to symbolize that only one option remains - that of מצא אשה מצא טוב. (A similar sentiment is brought in the Beis Emes [authored by the Lev Simcha of Ger], based on Eruvin 54)
Perhaps the custom originated from the halacha that the chosson is בוצע תחילה (See Berachos 47, Magen Avraham OC"H 167.29); he is the first to 'break the bread'. It is possible that in the times when they observed this halacha, everyone partook of the bread from the central loaf which the chosson cut.
Today, this halacha is virtually obsolete, because at our weddings the public begin the meal and partake of the bread before the chosson and kallah arrive, and everybody has their own roll.
