There are hundreds of moving parts within the engine of a vehicle, with the majority of them being made out of metal, it is critical that these internal parts stay lubricated to reduce friction and heat. Over time the oil in your engine collects dirt and soot from the burnt gasoline or diesel fuel, reducing the effectiveness of the oil itself; leave the same oil in your engine long enough and it can cause detrimental damage to the motor or even completely seize the motor. To keep your engine running smoothly, you must perform routine oil changes based on the manufacturer's recommendations.
Unlike oil changes, you will not necessarily be putting your vehicles health in jeopardy if you don't routinely rotate your tires, but you will be reducing the life of your tires. With most tires costing over $100 today, rotating your tires can help you reduce the overall cost of ownership by extending the life of your tires as long as possible. The front tires of a vehicle are going to wear at a different pace and in a different pattern than the rear tires due to the fact that they turn with the steering wheel; rotating your tires is going to help all four tires wear at a similar pace and in a similar pattern, extending the life of your tires.