There are so many reasons I prewash, I have lived overseas where a lot of it is made and seen how and where it was stored before shipping. Plus all the chemical's they put in the fabrics. Just last week I bought from several places and got home and was petting all my beautiful new fabrics before I washed them and my hands turned red and started itching so bad I had to start treating them with allergy cream. This had never been a problem for me before. I told one of the women who cut at one store about it this week and she said some time ago her husband had to come get her and take her to the emergency room as her hands started doing that and turned into blisters after she had worked with a new shipment. As a new sewer years ago I learned the hard way by having a beautiful project bleed and shrink. From that time on I have washed as soon as it came home with me.