The size scraps you save should be based on the kind of quilts you make. If you like applique really small can come in handy ( I never know when I’m going to need an eye, or a berry) if you like string quilts long, skinny strips are saveable. If you ever make kennel quilts ( or pillows, padded items those slivers, tiny pieces can be used as stuffing. )
anything You think you will never use you can pass on. I never send my scraps to a landfill, there is always someone willing to pay postage for what I have no use for.