I use for a lot of reasons, none of which, as you can probably guess, hold up in the light of what sometimes happens as a result. I do it because I'm bored, because I want to relax, because I don't want to feel angry, anxious or depressed and sometimes because I want to feel things I can't seem to access sober, like grief and contentment. I do it to sleep and to loosen up and to socialize because I've never been able to do those things well. I do it because, in short, I've become dependent upon it for a lot of things, and because I crave the chemical as well as it's effects.
Right now I'm working with a therapist to find ways to do all those things without alcohol or drugs, but that's always the clincher for me, how to do things without that crutch.