Here's a little quickie Pit Stop Procedure vid we created for those that aren't familiar:
The pit stop not only allows you a little break during your 15-minute main (or 10-minute main if you are a F2 driver), it also allows you to change your position on track, great if you are stuck in a heated battle or surrounded by traffic.
While some will argue that it does make it a little difficult to tell who's racing who on the track, the race director can get an idea based on track position, the scoring screen and the pit dots on the nose. Most love the pits simply because it does add a more authentic feel to the race.