I pre-wash everything except for pre-cuts like jelly rolls. I always buy quality jelly rolls like Moda and when making a jelly roll quilt it's all the same fabric so the shrinkage should be the same.
If I am adding other fabric to a jelly roll quilt it is likely from the same collection so I don't wash it either.
Otherwise, everything else gets washed, ironed and starched. I recently got a FQ set from Connecting Threads and I washed them. I was BARELY able to get two 8 1/2" (total of 17 inches) blocks across some of the the 18x22 pieces.