Anything I am incapable of using to sew into something is what I throw out!
I have just started quilting but I have always sewn something - my clothes, costumes, curtains, drapes, domestic stuff. I have always saved bought-clothes and bought-curtains if I loved the fabric, and then used them in other projects over the years. I like it because something which pleased me once can please me again, if only by being useful one last time.
I am specially saving all the leftover fabric from the quilts I am now making for my grown children, so that I can make a big scrappy quilt from them all and it will be like having a piece of them with me. :-) :-)