It might help to know what chassis you are talking about!!!
Rotors/drums are turned to create a smooth surface for the new linings. They get pitted, grooved, warped and rusty over time and use, especially if the original linings are well worn down. Some original linings were attached to the shoes using rivets and well worn ones can gouge the drum/rotor. There are limits to how much they can be turned and when turning would exceed those limits, you are in for new drums/rotors. Calipers may need replacing too as they are no longer being rebuilt in the shops.
Workhorse has an outstanding recall on this item, are you affected?