What is the purpose of Anti-lock brakes?

To maintain directional control during a hard or panic stop.

Think about it. If your brakes lock, you go into a skid and lose control of the car.

Anti-lock brakes prevent the brakes from locking up, and throwing the vehicle into an uncontrollable skid. This system allows maximum deceleration without having the brakes lock, which, in turn, allows the driver the ability to maintain control of the vehicle while coming to the most rapid stop possible.