A speedster can have a huge impact on a baseball game. However, mobile players are more than just guys that can swipe bases without a problem. They also have great range in the field, which gives them the ability to make plays that others cannot.
These players can serve as table setters for their team's lineup, and they can get a team out of a tough inning when they are in the field by tracking down a ball.
Mobile players are rare, and there is a reason why they are highly valued. They can contribute so much over the course of a season.