Not many racers do it now! but years ago we ran 2 line locks, 1 on the fronts for our burn outs and 1 on the rears for staging! Especially on the stick cars, Because when staging when using the front lock it would do exactly what Cobalt said! and with automatics we could carry the r's a lot higher with the rear staging lock!! And in gas class most of us had no front brakes so we could only use a rear staging lock!