Why is that important? Because when a brake rotor doesn't spin true (or warped), it will contact the brake pads twice each revolution (when your foot isn't even on the brake pedal!). Over time this wear will cause the brake rotor to become unevenly thick and cause unwanted pedal pulsation and affect overall performance of the braking system.
WHAT WILL THIS DO FOR MY BRAKES ????
Many cars, even from new, have minor brake hub distortions. The Pro Cut lathe takes a tiny skim
from the surface of the new discs to remove any hub or chassis misalignment that may exist on
your car and would cause brake vibration after a few thousand miles. Brakes feel smoother and
last longer. NO vibration