1: Keep em from looking like the old woman on jackass number two: Very saggy and looks like a sock with a tennis ball in it (look in a national geographic mag, ugh, of course they are women who never wore one in their whole life).
2: To help eliminate severe bouncing action when the female walks, runs, or dances. They can be quite cumbersome without one while running. Because big ones can hit the face! But the male seems to be entertained by watching this action due to their enthrallment of big, round, firm, and tanned Breasts.
"WOW! I Went from an "A" cup bra to a "36 C" cup bra, all in the 7th grade!"
"you motorboatin son of a bitch" -Vince Vaughn- (with no bra)