I try to buy what I need or going to use for my current project. I rarely buy just to buy or for a "someday" project (although, I do have a stash of 30s repro fabric, but I really do have a project in mind) I look at the unused fabric and I see dollars that I can't spend.
often I look at what is on my shelf and I no longer like it. It looks so dated some of it! LOL!!!
I actually get a kick out of using the last piece in whatever project w/ no remains. My current project will be that way.