Why is your pubic hair brown?

Pubic hair is a lubricant. It prevents skin to skin rubbing and irritation during sexual intercourse.
Pros:

Pubic hair helps keep the female scent in their body. It also reduces friction to the area from the clothes preventing arousal at the unwanted times. It prevents dirt and insects from getting into your area.

Cons:

Pubic hair can also keep disgusting stuff in your area when it's your time of the month. The pubic hair can keep moisture in your area increasing your chance of having a bacterial infection (yeast infection). If you are wearing lacy panties or things and such, the hair gets in the way of your straps and laces. A lot of pubic hair can cause your mate to not be able to see what he is doing.

For guys, there really is no reason to keep it except that it's a lot of work maintaining that shrub. It also gets in the way of blowjobs.