I am one of those wash everything first people. If you know the quilt you are making is going to be washed frequently, ie. a grandchild who loves on it a lot, I say wash everything first because as you already have found out, some fabric shrinks a lot and some very little.

I'm a pre-washer. Not only because of the possibility of shrinkage and dye-runs, but because I personally find that the fabric 'sheds' less if it is pre-washed (I realise that this goes against accepted thinking, but it is what I have found from experience).

I very rarely buy pre-cuts - I have never in my life had a jelly roll (and never will), used a layer cake once, and have 3 charm packs I have not yet used. But I would not prewash those. Not because my reasons disappear, but because I would anticipate more distortion and fraying with little pieces. Just means I am careful about what I would use the pre-cuts for. And I wouldn't mix washed and unwashed fabric.

From the general response it would seem that pre-washers do not tend to purchase pre-cuts as much as others.

I think it's safest to pre-wash all fabric. I don't buy pre-cuts because if you try to wash them it turns into a disaster. There's so much shrinkage, fraying and distortion of the shape. I do buy fat quarters because I can re-cut them. I like to do my own cutting.