I have washed sometimes and not other times. I got a load, I mean LOAD of fabric about 10 or so years ago, from someone who didn't want it anymore. (I never met the person, the fabric came through a third party.) I could tell which were washed as the ends were terribly frayed. She must have washed with an agitator washer for 15 minutes.LOL
Sometimes I wash and sometimes I don't, and have never noticed the difference in the finished quilts. My thought is: this fabric has a nice sizing on it which makes it very easy to cut with our rotary cutter and is easy to sew because it is a little stiff. Then we wash it and it gets limp, so we have to starch it so it is easier to cut and sew. ? ? ? Does that make sense?