Thanks Scott...this is a great basketball drill for many reasons.
First, and most obvious, it works on the footwork for the defensive slide. That's the most fundamental element to playing good defense.
Second, it works on the drop step and slide. This is often overlooked by coaches and players, but the drop step and slide is a critical part of playing man defense.
Third, it works on conditioning. As the players are sliding, they are working on their stamina and conditioning. But also as they sprint down and jog back, they are getting even more conditioning.
This is an excellent basketball drill because it works on a variety of skills needed to play great defense.