Dribbling a basketball at full speed is a much different feel than walking up the floor or being stationary, and it is a lot more difficult. What is even more difficult than that is being able to change direction with the basketball going full speed. One of the best players in the NBA at doing this is Ty Lawson for the Denver Nuggets. His ability to get up the floor and through traffic in transition allows the nuggets to play at a very fast pace, and it makes them very hard to guard.
The 1 dribble between the legs change direction drill is going to help the player work on being able to make a move at full speed, while still staying under control. It is okay for the player to lose the ball during this drill as well, because it means that they are getting out of their comfort zone and pushing themselves. This is actually encouraged in all of our basketball dribbling drills.