Today in intro to coaching class, we learned that every anaerobic function - lactic or alactic is dependent on the aerobic system. By developing the aerobic system you are able to recover from jumping up for a rebound to get the ball on defense, then to be able to do it again on the other end when you slam dunk it.
Obviously anyone can recover from this once or twice, but if you are jumping all game, and your max height barely allows you to dunk in the first place, then you will have trouble at the end if your aerobic system isn't developed a decent amount. Obviously you have to balance things out - too much cycling and you become a cyclist - not a well trained basketball player.
Obviously using dunking as an example is easily flamed. But if you can jump 1 inch higher at the end of the game than you would have it could mean the difference between a turnover or not.
It's important, but it is important to balance it - you obviously don't want to do it to the point that it hurts your vertical jump a great deal. (which would mean doing a lot of it, a lot more than an hour a day, assuming you do stuff to keep your muscles strong ie weight training.)