The cooling system in your vehicle is very important. Coolant comes in contact with the engine, flows to the radiator, cools down, then heads back to the engine to pick up more heat. This cools things down under the hood and ensures heat is distributed evenly so your engine performs at peak performance levels. However, your cooling system is only as efficient as the coolant that's in it. Coolant is constantly being used and its heat carrying abilities wear out over time.
Each manufacturer recommends coolant be changed at different intervals per vehicle.