The wheels of a car and especially the tires are exposed to lots of stress. The rubber itself degrades after a certain time. Many tire manufacturers have in fact recommended "life times" regardless if the mileage is reached or not.
Nevertheless tire dressing makes the wheel clean, glossy, and overall the car much more appealing. However, using the right type of products could actually help your tires from early retirement (note that they can NEVER extend the life of a tire or prevent failure from physical stress). Some products however claim that they can help protect the tire agains the elements, especially the sun. Protection could extent to helping prevent cracking, fading, and hardening of tires.