I smoke for a number of reasons.
1) To get high. Just to feel the euphoria, sometimes just to stave off boredom.
2) To relieve stress. College isn't all fun and games, and sitting down to smoke a bowl in the evening (or the morning, or the middle of the night, or the afternoon, or my lunch break) helps me enjoy that free time in relaxation rather than worrying about the shit I have to get done or if the shit I got done was done well enough or if there was some shit I should have gotten done but didn't.
3) Appetite stimulant. I don't really feel hungry that often when I'm sober. I'll get a vague feeling of having not eaten in a while, but any feelings of actual hunger are pretty mild and then I can only eat a little bit before I just can't get myself to eat anymore. But when I'm stoned, it's a whole different story. I could eat four plates of food and still scarf down dessert if I've had a nice session beforehand (which comes in handy at the all-you-can-eat buffet style dining halls we have here).
4) Music enhancer. 'Nuff said.
5) Because I can! I really don't have much else to spend my money on (when I have money that is) and I also get significant amounts of free weed from a friend of mine, and life is short, so why the fuck not?