I don't pre-wash pre-cuts. I'm too lazy to do the delicate work of trying to wash those babies without them fraying or distorting, so I just use them unwashed and cross my fingers when I toss it into the wash for the first time (with a wad of color catchers). So far I've been lucky, even when using batiks.
I also don't pre-wash things like canvas or random remnants I pick up for making tote bags - I consider those to be "utility" items so I don't really care if things run or shrink a bit as long as I can still drag my groceries around in it. I've also started a denim & fleece scrap quilt and I haven't been pre-washing either the denim or the fleece. It just didn't seem necessary. (Though a lot of the denim is from salvaged jeans, so very well pre-washed in that case, but some of it is new remnants which I have not been washing.)
I don't pre-wash wide backing fabric before stashing, either. I do pre-wash it just before I use it though, and I'm glad I do as I've had some pieces shrink quite a bit. (I wait to wash just before it'll be used so I don't have to FOLD the giant things!)
I wash most everything else, though, despite what a chore it is.