There are two things I make them run sprints for. The first is for not using two hands when catching the ball.
Good point by chinamigarden.
It's good to catch the ball with two hands if you're able to get in front of the ball. Otherwise, catching with two hands can limit your range. I've taught to stop catching with two hands on certain plays. Running catches in the outfield should almost always be caught w/ one hand, IMO.