Probably at least it deters spammers if they have pic ads. Someone might get banned and decides to make a new account just to give out neg rep in retaliation.

A lot of places automatically have new users on probation. The user actually has to be here long enough to get a feel for the rules. That way you won't see many offensive oversized sigs, offensive pics, and neg rep for no good reasons (of course you still will occasionally). It's a privelage, and it shows its something that shouldn't be taken for granted.