I prewash usually. But it's for shrinkage or because I buy a lot of fabric on estate sales, garage sales, thrift stores, etc. and don't want to take any chances of animal dander, smoke, musty smells etc. Bleeding? I use a color catcher when I was them but if something bleeds on something else I use it anyway. With today's blenders and batiks and wild fabrics who will know if it didn't come that way. I don't make show quilts so if there's a little bleeding it won't effect the warmth of the quilt, I don't care. Maybe I should but I just don't. Once it's quilted, on a bed and someone is under it no one will notice anyway.