The reason we have hair is to protect our bodies from dirt and other pesky things, one of the speculations on why humans are less hairy then others species is because we learned how to clean ourselves and fashion clothing making hair less necessary because we didn't need to protect from the cold with clothing and didn't need to protect from dirt and the like because we learned to clean ourselves. A different theory is that humans are nasty little fucks who got lice so bad their bodies were just like fuck it and somewhere in the evolution we lost hair because of being nasty little fuckers.
Hair also makes a good cushion for when you're pounding the ladies and you don't want to smash her pelvis.