pubic hair is made to collect and then give off smell. it is flat because that gives it more surface area in which to give off smell. it is around your pubic region because that is where you secrete an oily odorous substance that collects in the hair. the opposite sex would be attracted to this smell but we in modern society are trained to be more repulsed by body odor. your under arms are nice and stinky too and the hair around there collects it and advertises your smell. shaving the underarm hair or trimming it would reduce the effectiveness of the smell broadcasting. we are supposed to like the smell but in modern society this shaving or trimming technique can be employed to reduce the odor.