If you have two drivers, they can compare their laps and see where each one gains or loses time, and why. A driver can compare his best lap to other laps and see where the difference is. Drivers can try different techniques or styles and see what difference they make. Several customers report substantial improvement in lap times from analyzing braking performance alone. Engine data can be very helpful for increasing both performance and reliability.
Some racers also monitor fuel pressure and nitrous pressure for the same reason.
One customer reports that the system saved him an engine, by showing him a problem before the engine was destroyed. Engine RPM is a big help, especially combined with g readings and throttle position. In any class where you can change your gear ratios, this is very important to be competitive. A tach with a telltale might tell you that max RPM was 8200, but you don't know if that was once, or every lap. The Corsa system can find the exact engine RPM all around the track.