Being able to handle the basketball on the move and make a dribble move is a different feel than standing stationary and making different moves. This basketball dribbling drill is going to work on making a behind the back move while moving forward up the floor, but it is also going to add to the difficulty of the move by adding and extra basketball.
Using two basketballs will help to work on a couple of different things. First it is maximizing time because the player is working on both hands at the same time, but secondly it is eliminating the players ability to switch the basketball to their strong hand. Too many players are one hand dominant when handling the basketball, and as soon as they get into trouble they immediately switch the basketball to their strong hand. Two ball basketball dribbling drills eliminate this option. This is a great drill to do at the beginning of basketball training to help get the player warmed up before getting into full speed movements.