For myself I keep pieces 1 1/2 inch by 3 inch or squares 2x2inches. If I do not care of the fabric or know some one wants it I give it away. I am trying hard to keep abreast because I need a space that has some organization inorder for me to be creative and enjoy quilting.
Waste seems to depend alot on what size fabric you started with and the pattern you are using. I have way more waste from applique and fuzzy cutting then when I cut strips or squares.