Rotors are made entirely of metal. The PADS are not. On any brake job the rotors should be “turned” or machined smooth in order for the new pads to seat well and wear evenly. Today’s rotors are thinner and lighter and usually are replaced after the second turning.
A good brake shop will do these things since they don’t want you coming back saying that the brakes squeal or stop with grinding noises and vibration.