I'm lazy. I prewash, that way I don't have to think about it. I also know that after I prewash it, anyone who receives a quilt from me won't have to worry about washing the quilt and ruining it. Any damage likely to occur to the fabric has already been done by me.
I just run a quick straight stitch along the cut edges of fabric before I wash them. It doesn't take much time and saves a lot of raveling.
Rodney