As the engine heats up, internal engine components expand and contract. Since engines are composed of different materials, each material expands at different rates. Manufacturers design engines to have space between components so that the various components can rotate and function. A valve adjustment is necessary to maintain proper valve clearance.
Most manufacturers have their own specifications for when to perform a valve adjustment. If proper valve clearance is not maintained, then the engine components may wear prematurely. If the valve clearance is not correct then the engine's intake and exhaust valves can fail prematurely, causing idle and drivability problems, and excess pollution.
When performing a valve adjustment, the technician removes the valve cover and manually rotates the engine. Then each valve clearance is measured and adjusted accordingly.
It would be best advised to follow the factory recommended vehicle maintenance schedule for how frequently a valve adjustment is required. This factory recommendation must be adhered by to maintain the validity of your new car warranty and extended auto warranty, if applied. If mechanical breakdown occurs due to the lack of your car's maintenance of the valves, the warranty would not cover the car repair.