I make quilts primarily for charities and would never think of making and sending one off without prewashing the fabrics in it. (And the quilt itself when it's completed). I don't want to donate anything that might sicken a child from the chemicals in the fabrics, or have the various fabrics shrink differentially or bleed from one color to the other and become a depressing mess. I think for wall hangings and other things like art quilts that are for display only that aren't needing to be washed and dried, then of course not prewashing is reasonable if we want to keep the fabrics new-looking.
Dana