There is no denial to the fact that every fielding position on a cricket ground has its own merits and demerits. Different part of the ground require different abilities. Having said that, fielding at short-leg is a decision which involves not just the ability but a handsome amount of courage as well.
The primary reason for the same is the limited amount of time that a short-leg fielder has to react to a ball. Since, the speed of the ball is inversely proportional to the time, it is really important for a fielder fielding at short-leg to be on toes all the time.
A short-leg fielder predominantly comes into play during a test match. It is a stage where the fielding captain can afford to have these attacking fielders. Watch the video to see some sensational run-outs by short-leg fielders:
https://www.youtube.com/watch?v=qcd67BbpbY0