This may be an old subject, however, I almost always prewash my fabric. Since we've downsized from a house to apartment, my fabric is all in totes, some of which were in my basement sewing room for an undetermined time. At times I would not prewash and iron all my fabrics when it went into the totes, but when I was going to use it, I washed the fabric in cold water and dried it in the dryer. Yesterday in fact, I pulled a large piece of black fabric I planned to use as a border for our black/white family reunion quilt. Since there was a bit of odor, I took it to my bathroom sink to rinse out. I'm very glad I did because even though the fabric had been washed and dried previously, I still had some color bleeding through to the water. Since the fabric is still somewhat damp, it will be easier to iron dry before I cut it up for a border. I don't always wash small remnant and fat quarters, but if I do I put them in a pillowcase and close it with a rubber band. Besides keeping them together, all the threads are contained to the pillowcase. That's my opinion on the subject, however, I'm sure it will be debated for years to come.