The cambelt, also called timing belt controls the timing of all the key moving parts in the engine such as pistons, crankshaft and valves. Many car engines are fitted with belts made of a rubber like material, which have a limited life span. Car makers will recommend when the belt must be replaced.
If it is not replaced at the right interval (mileage/age) it could easily break or come off, cause severe damage to the car’s engine which, in many cases is terminal. This will be very expensive to fix and could be enough to write the car off.