When I cut my scraps I cut the largest square I am able to and work my way down. Generally the smallest I cut is 1 1/2” square. Or 1 1/2” x how ever long.
I think it is best to think about what kind of quilts you make- what will you use. If you do appliqué small pieces can be useful but if you only make big block quilts you probably won’t use those little pieces. If you are interested in making scrap quilts then check out the website for a scrap Quilter ( like Bonnie Hunter) they generally have a * system* and usable size range they recommend.