I took a quilt class once where the instructor was adamant that you had to wash. So I washed.
Then I took a class from a very good instructor who had her own quilt shop. If you bought the fabrics from her for her class, she waived the fee for taking the class. You just showed up early for the class and bought the fabrics. I asked her how this would work for pre washing and she thought I was crazy. So I tried it and I have never pre washed since.