My criteria is as such...the obvious ones:
1. Title was purchased during the Truman Administration, scores & several parts are missing, and is POP,
2. Older title has been superseded by a newer and better arrangement,
3. Older title that was, quite frankly, a piece of junk to begin with.
Of course, I would be keeping anything on the PML, or has been recently been removed (we all know of pieces that have been on, then off, then back on the PML before). I am not looking to turn my library into a "PML Only" library as there are indeed good titles of all styles that aren't on the list. At the same time I have a LOT of things that are more than likely never going to see the light of day ever again...not even for sight-reading practice.
What do you take into consideration when cleaning out you library?