I've always regarded them as parking brakes that can be used to stop the vehicle if your regular brakes fail. As a parking brake they should hold the vehicle in place even on a hill. If they won't do that they need to be adjusted or serviced.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.