Answer- Everything: pads, rotors, calipers, hoses, lines, master cylinder, booster, shoes, drums, wheel cylinders, return springs, hold down springs, parking brake cable, self adjuster, brake lights, the whole nine yards. It's your responsibility to make sure people are safe on the road and they are aware of the condition of their brake system.
Yes, it's true brakes only slow you down. Even though we may be speeding down the road at 80mph eventually you will arrive at your destination: home, the mall, the grocery store, your Aunt Krusteaz house. Once you've made it there and are ready to slow down for some of her famous buttermilk pancakes you'll probably need the brakes unless she's been discarding all her left over batter in the front lawn for you to slide your car into.