Some people just prefer to use it to fine tune any minor understeering issues. Because as you turn at slow speeds (where caster is noticed the most), you should be able to tune caster in order to give a better 'loose' feeling when turning in a slow corner. You will find hotlappers do this just to gain a bit of time in the slow spots. For example on Aston National, the tight set of two corners is crucial for time gain in a GTR car, so you will notice a bit less than maximum caster on hotlaps setups. It is better than having to lower your overall camber, because that would hurt your highspeed cornering. I think caster helps the most for FWD cars, where you need to feel loose and flat to get the power down... because excessive camber while accelerating/exiting a corner, not good. Also the higher the caster, the most pesky the steering becomes with its sensitivity at slow speeds (In other words, the highest you go, you will find a quicker grip-loss point as you turn the wheel farther and farther.... whereas lower caster it will be more gradual transfer into understeer the more you turn the wheel to its extreme, conserving the tires).