if you want to corner quickly, you should neither utilize under or over steer. in each your car is losing traction. there is a proper line to take any corner. you need to brake in a straight line leading into the corner. start your turn, and you should hit the apex of the turn on the furthest inside corner. from here, you can exit the turn and begin accelerating. this will lead to fastest times.

cars are built to have mild understeer because it is much safer driving and easier to control. if you ever drive a RWD car with a decent amount of power, you know that if you are midturn and hit the throttle the back end will come racing forward on you.

on a rally course, the reason they utilize oversteer is because the cars are built to gain traction in any condition. therefor, they do not need to slow down, they can spin the car in any direction they need and gain traction immediately. if you try this on a road car, you will most likely end up losing control and spinning back and forth as you try and gain traction.

 

Yes, what you said about taking the correct line around a corner with all the correct methodology involved is just what I said a few posts back; just with more detail. However, I wouldn't say that rally racers utilize oversteer purely because they have these super state-of-the-art machines that can gain traction more quickly then your average car (which IS true), but it is due to the track conditions on which they are racing. While driving an ORDINARY car on a rally-style track or road, you would still benefit from oversteer when going around those extremely tight corners you would encounter, provided you are very competant with controlled oversteer. On pretty much ANY other track, though, oversteer is PURELY for show and yes, faster lap times will come from keeping all 4 tires in traction and taking the correct line.