I have come to notice that only a small ratio of materials I own actually sees play. Accordingly, I will often by the pdf, but hold off on printing something out or buying the hardcopy until I know I am actually going to use it in the game. And then, I try to only print out the snippets I need (in some cases, if it's just game prep stuff and the players don't need to see it, often I don't print it out at all and run it off the laptop.)