because your foots slightly rests on the brakes whilst driving, on a manual your right foot controls brake and accelerator and your left foot controls the clutch only. therefore no brake wear as your foot is switching between the two.
if you rest your foot on the brake whilst using the accelerator, you dont realise that you could be overheating the brakes, which can cause brake failure and accidents. this is why there is a foot rest in the left hand part of the footwell for your left foot to rest upon