I do a lot of charity quilting using 6" squares. I use that size, because it is to easy to cut them quickly with the 6" x 24" ruler. Sometimes I use them in D9P, other times just in 4 patch blocks. I always have some to work with when needed.
Smaller pieces are kept by color in string bags. Long pieces trimmed from the edges of quilts are saved for possible use as binding if wide enough.
I do a lot of scrappy quilts, but if the color or pattern aren't what I want, I pass them along to someone else.