I've done some movies because I would regret them if I didn't, but other projects I've done because they've scared me or if I felt I needed to do a big romantic comedy to help me professionally. Then I'll take a teeny movie when I need to work on myself and become a better actor.
I've never smoked crack. I've never done most things, drug-wise. But I assume that the experience I had watching Lost is the experience that crack addicts have smoking crack.