I am not a prewasher - mainly because I don't have the time to wash, dry, THEN IRON the yardage out in order to use them for my quilt. There is the raveling - and i really don't have the time to serge or zig zag the edges to prevent/lessen the raveling.
The only exception would be using red and white...but then I take a piece of the red, soak it in some water to see if it bleeds before washing. Then I also use some color catchers when i wash.