Anything less than 1.5" gets tossed. Moving upwards, I'll cut leftovers to the largest size that the fabric allows: 2" strips or squares, 2.5" strips or squares, 3"... Anything 4" or more goes back into the "up to fat quarter" bin. You never know when you're going to want/need that weird border...
I don't want to cut down fabric prematurely. I would rather keep it in the largest size it will allow.