I tend to have a different view than many mechanics and users when deciding what to do with rotors and brake drums at brake pad/show time comes along.
Unless you live in the rust belt and they are very rusty, I normally will not be too concerned about minor grooving, especially on drums in the rear. Runout is a concern for sure, and on rotors much more so than on drums. If they aren't badly grooved, I clean them up a bit, and make sure the rotor to wheel hub mounting surface of the rotor and hub are totally clean, burr free, and with no rust or other bumps on them. I have found that well over half of the rotors that showed excessive runout before removing were fine after the cleanup. The problem is usually that people or shops remove a wheel for some reason and the rotor comes loose on the studs (yes some have two screws that hold them in place which prevents problems, but on older cars they are either missing or the car never had them) and rust or dirt fell between the rotor and hub surfaces and caused runout.
If a rotor checks within spec for runout and has minor grooving I will just sand the surface to give a clean break in surface for the new pads and use them. Turning a rotor that doesn't really need it may make it worse after a small amount of use because the turning lowers it's thermal mass and also relieves the surface stress in the metal surface and that can make it prone to warping when it gets hot again. I have also, like many of us, found that the currently available new rotors can be very, very bad right out of the box and need turning to be usable. You have to a least mid, but often higher cost rotors to get good material and runout in them. I ran the original drums through 5 front pad replacements, 170K miles, on my 92 Escort. I only replaced them because we are in salt country and they started to get so rusty they were in danger of having holes though them. They still ran true and had never been turned.
Drums are a bit harder to check runout unless you remove the backing plate but on the rear doing a spin test to see if they hit hard enough to stop you from turning them easily through minor rubs is normally OK and even new, high quality drums, if you can find some, will often give a bit of rub. Again, clean mounting surfaces and a good fit at the hub center are essential to get good runout.
One old school thing that is still done is to index the drum or rotor on the studs to find the lowest runout point. It does work, but you have to be sure to mark the rotor or drum and the stud so you always get them back on correctly in the future.
