I prewash all of my fabrics -- except for kits and jelly roll, only bought one of each of those.

I always pre-wash, but, I have lots of allergies, so everything that is made of fabric gets washed as soon as I bring it in the house. I talked to the ladies at my local fabric store (lqs) and I was told that most people don't pre-wash anymore, so it is a personal decision. Good luck!