So many chose slice backhand deep approach... hmmmm. Unless it was also sliced wide at the same time and with a certain degree of side spin, I don't think it would be as effective as maybe one sliced short. A slice that lands deep has a higher chance of having a higher flightpath and bounce, so if the direction wasn't too good, an opponent not in nomansland will require less time for preparation setup without having to scramble forward, and the bounce may even be sufficiently high to execute a topspin lob return. Even if we're comparing wide slices, a short one will probably be more practical than a deep one, since more distance needs to be covered by the opponent to reach the ball. A proper slice short will usually stay fairly low. The key of the approach shot is to weaken the opponent's return so you can come in and do good volleys, rather than defensive ones. BTW if you're thinking about deep slices as in fast German slices SteffiGraf-style, 1 you are increasing your error percentage of your approach shot, 2 you have less time to close in to the net.