I prewash everything before it hits my sewing room. I do it mostly for the bleeding but I think it is more habit then anything else. Also I get a great deal of satisfaction when pressing my brand new fabrics before folding them and putting them away. I love looking at a big 'ol hunk of brand new fabric splayed across my ironing board. I seem to notice colors and designs all over again and in more detail then when I purchased it. Even more so if it was an on line purchase.