Like others here I save strips I consider useable, ie. at least 3/4"-1" wide or more. My selvedge strips are all too small to be used for much of anything (typically less than 1/2" wide and only a few inches long) so they get tossed along with the trimmings from straightening the width edge of the fabric. If something has been cut really poorly and there's a section wide enough to use at one end I will probably keep that part.