If the opponent is way out of position, a short slice works just as well. Yeah, it is not as short but it is faster so it probably bounces twice in a shorter time too. It is less risk and easier to hit. Even if the opponent reaches it, it is less subject to attack. If the opponent is not way out of position, a drop shot is almost always a bad idea unless he really sucks. Well in that case you can win do anything anyway. So I don't see any situation where a drop shot is the best choice of shot. Of course if you are one of those people who is really talented with the drop shot then go for it by all means.