Are you refering to how to handle topspin/slice or if you should hit topspin/slice?
Hitting topspin gives you a couple of main advantages. It isn't as much about what happens to the ball when it bounces but how it travels through the air. A ball struck with topspin when traveling through the air will drop more quickly. Try tossing a beach ball to a friend. When you make the circumferance of the ball bigger the affect is more pronounced. When you toss the beach ball do it a couple of times with underspin (slice) and a couple of times with topspin. Notice how the ball takes a nose dive when you throw it with topspin. This gives us the advantage of when you hit it, you can hit it harder and with more height (Less chance of hitting it in the net and creating more depth) and have it still drop into the court. Slice is great for keeping the ball low when it bounces, but your clearence over the net has to be very little to get it to slide and your percentage of it going over drops when your target is so low.
Hope that helps or answers some of your question.
Mike Burge
USPTA Master Professional
www.dynamicdoubles.com