If you're a fat sloth who can't control his diet then I wouldn't consider using steroids. Conversely, if you're skinny as a twig you probably don't have any business either. Generally speaking, that is...
I think people shouldn't be anymore than 12% bf before they should hop on the sauce because the more bodyfat, the more bloat. You don't want to take tons of anti-e's because estrogen is a great bulking agent. You want to have a nice buffer instead of struggling to look half decent. Nothing more embarrassing than taking steroids and looking like shit.