I do some version of that (what the OP said), though I usually cut them into strips, or chunks that get used in improvisational quilts or other art pieces. Some of my best quilts have been made from cut up UFOs. I also use them for FMQ practice. I figure if one has really gotten to the point that I don't want to finish it then it's the same as all the other fabric in my stash, more raw material waiting to be played with
Rob