To me, a scrap is anything I won't use in something else.
I try to figure out what size block I use the most, and then cut up my odds and ends to sizes that can be used to make those size blocks. If I make 6 inch blocks, then I will cut my odd pieces of fabric into 1.5, 2, 2.5 , 3.5 and possibly even 4.5 inch squares. Then I can use any assortment of them to equal 6 inches.
For strips, it has to be at least 12 inches long before I will consider it a strip, if it isn't that long, I will cut it into squares. I will cut strips the same widths as my squares.
I always try to cut the largest size pieces out of my odds and ends first, then work my way down to the smallest sizes until I can't get any more pieces at the sizes I want. Anything that is left over, gets tossed.
If you do any needle felting (hand or machine), and can use small bits and pieces with that, then I would keep even those small pieces to add to your stash of embellishing supplies.
Diane in Colorado Springs