If light is on, it indicates the cruise control is controlling your car’s speed. The cruise control should turn off as soon as you touch the brake pedal. If the light remains on, there is a serious system problem and it is NOT safe to drive.
Usual problems: brake pedal switch connection, electrical problem, defective electronic unit
The purpose of a cruise control is to automatically control the speed of a vehicle without intervention from the driver. Cruise control takes over control of the throttle. It is useful for long drives by reducing driver fatigue and improving comfort. If there is any cruise control problem, visit an auto service center as soon as possible.