After watching a number of tutorials, I wanted to make sure it wasn't absolutely necessary to replace drums when I replace shoes and springs etc (I'm on a budget). Can someone confirm this and/or recommend best practice? Safety is obviously important, but maybe this question is rooted in misunderstanding.
You don't need to necessarily change out the drums, but there are a couple of caveats to this as an answer.
If the drum is in good shape and meets minimum thickness, you could just put the old ones back on there. They will not work as well as if you did one of the following two routes. You'll still need to bust the glaze on the wear surface of the drum using some sand paper or something similar.
If the wear surface of the drum is rough (you can feel ridges when you run your fingernail over it), you'll at a minimum need to get it machined so a fresh surface is there. You can do this as long as the drum meets the minimum thickness needed for it to work correctly.
If you cannot machine the inner surface, you'll need to replace it. Most drums have the maximum diameter the machine surface can be. When you take it into get it machined, the place where you get it done can check this for you.
Whether you use a freshly turned drum or a brand new one, you'll find they will work better and your brakes will last longer than using a used one. Even minor blemishes on the machined surface will wear the brake shoes faster than if you just bust the glaze off of it.