Baby burps. If your baby is a "gulper" when she eats or if she has had a spell where she cried alot, she has swallowed more air and needs more frequent burping. There is not an exact right number of times, but remember, air that doesn't come up as a burp comes out the other end as - well, you know what!
0. "necessary" is too strong a word-- it's never "necessary." babies will do fine without burping, though it's traditional to do it. It's a nice way to put a pause in a quick meal, and might help a fussy baby feel better. But it is not something that parents should think of as crucial or necessary.