This is a really good tennis ball dribbling drill to help you work on your handles, but also push you out of your comfort zone. By adding the element of competition you push the players to go even faster then they normally would. There will be more mistakes, but these mistakes are good because the players are trying to go faster then they normally would.
The reason this is good is because when they slow back down to normal speed, they will be even more comfortable handling the basketball. It is important that when you do different basketball drills, especially ball handling drills, you are pushing yourself and challenging yourself to get better.