Check engine light, a discussion.
Each wheel of your car is equipped with two of these brake pads that close together when you press on the brake pedal. Naturally, these pads wear down over time. That metal scraping sound that you one day start hearing whenever you press on the brakes is your car telling you that brake repair is needed. You could choose to ignore the sound, but the pads will wear completely away and only metal against metal will be left to stop your car. Only metal is left after the pads are gone, and continued use will ruin the wheel mechanism.