I was prescribed it because the antidepressant I was given (Wellbutrin/Bupropion) made it harder for me to sleep.
Indeed, it's really sedating. That can be a good or bad thing depending on the purpose. I took it before I went to bad and it instantly knocked me out. I couldn't imagine going through the whole day with that in my system.
The only problematic side effect that comes to mind, is weight gain. It affects your metabolism. It won't be that much of a problem if you keep at a good diet and exercising routine, but... still.