I was a heavy user all through highschool I use to smoke out atleast 5 times a day. Now, I only smoke once maybe 3 times a week or I can stop if I want to. I think I went through some kinda of phase.
To relax, reduce stress, etc. It cannibinoids can also increase hunger (which can be good or bad depending on your diet/genetics/etc.). It's great after a hard workout.