Cheek pads can wear out on any helmet after prolonged use. This affects the fit of your helmet, and greatly impacts the amount of protection your helmet will afford in the event of a crash. A helmet should fit snugly, without "wobble" or "play" on your head. Wear isn't the only thing that can prompt you to get new cheek pads though. Sometimes a Medium feels too tight, but a Large feels a bit too loose. In this case, you should be able to purchase a Large helmet and buy thicker cheek pads to achieve proper fit.
