Master resource purging
Basically, you should mark all resources you create _except MENU resources_ as purgeable. CODE resources should be left the way that FB sets them up. Don't change them.
You should also mark anything that the system is going to use as non-purgeable. I was just reading up on an interesting bug in WDEF, CDEF, etc. resources--apparently some commercial applications have these resources marked as purgeable and this causes crashes on quits or context changes. Using ResEdit to mark these resources as non-purgeable fixes the problem.
This is good advice, but there are also a couple of other things to consider:
That's a good point. Although I can't think of a case where the average FB programmer would have to worry about how many masters his program uses. Maybe in an application like a resource utility such as ResEdit or something like that it might be beneficial to clean up after yourself where masters are concerned. But I think for most people, making the resources purgeable is all that is needed. I could be wrong...