I have never si'd out of addiction to it, imo. I can go weeks without doing it and be perfectly fine. When I do do it, i'm usually feeling particularly low (self loathing) or stressed out. And its really just a release that relaxes my whole body - it just doesn't satisfy me until my emotions have been allowed to build up.

I don't know if this counts as a reason or a need - I think it falls somewhere in between. I'm not really sure why I do it, but I like that I have it as an option.