As previously pointed out, a narrow slip is usually found on one that is short. If this is the case, even if your boat fits from side-to-side with no problems, its bow may extend into the access channel, which I think may lead to more problems.
Second, having additional maneuvering room in a wide slip can never be worse than the lack of maneuvering room in a narrow slip. IMO, the only downside to a wider and longer slip is usually ''cost''. As in most thing one buys, "you get what you pay for".
~ Happy sails to you ~ _/) ~