I always prewash one ruined quilt was enough for me. Besides I have developed an allergy to the finish on the fabric. I hate sneezing while trying to cut . I like all my fingers where they are. lol
I even wash all my new fabrics together since I discovered the Color catchers. They go in my machine with all my new fabric and clothes.
I just washed some blue fabric with white and no color on the white but the color catcher was dark blue. I did it as a test .
Love those things.