i've made a few hundred quilts over the years- i have never (can not even imagine) pre-washed a batt. there are a vast variety of batts on the market- some shrink= some do not= some shrink alot- some very little- some are lofty- some are flat- some are best suited for machine quilting, some for tied quilts & some for hand quilting.
check with some of the companies & pick up swatches- which you can experiment with & try out to see what you like, don't like-
every time i show a picture of a quilt it's been washed if the binding is done- it has not been washed if it still needs binding.