Why do people feel the need to spit?

I go to university and in the morning, in the bathroom, kids seem to fit hawking loogies into the sink into their wake-up routine. Also, they just seem to spit while outside, onto the grass. What the hell? I honestly don't spit, ever. I don't understand why people spit. My roommate spits into the trash can by his desk a ton, and I grimace whenever he does it. It's a damned gross sound and I don't see how it benefits you.