Another reason for wraps (or weighted gloves): they absorb sweat. I usually use 1# weighted gloves when I do kickboxing (I worked up to them, so don't anybody just jump in and start using them for a whole workout right away!), and when I don't, my hands will get uncomfortably sweaty. It just feels yucky to make a fist with a sweaty hand.
Also, you can get wraps in different colors. I have black, red and yellow (though I now usually use my gloves, because wraps are quite a pain to wash and dry without getting them all bent and/or tangly).