I put anything less than 3/4" into a plastic bag. When it gets full, I will offer it to anyone who wants to use the pieces to make art quilts. When I see tuts of people using their rotary cutters to make shreds, I think maybe my shreds would be valuable to someone.
For me, I save 1" to 2 1/2" to make string quilts and squares from 2" to 7". I am still somewhat of a beginner, though and, so far I am not overrun with scraps. I have mostly 6" and 6 1/2" squares right now because I like to make I Spy quilts.