There really isn't any rule that you have to follow. I always pre-wash,but I have allergies, so I have to. Some people don't pre-wash anything. Some people find pre-washing to be tedious, but, I don't. I just throw the fabric in the washing machine and then the dryer. I don't iron until I'm ready to use it. That way I know that the fabric is done with shrinking,bleeding,etc.,before I put it in a quilt. It would really irk me if I had completed my quilt with unwashed fabrics and even with color catchers it bled and ruined the quilt. But that's just me. Do what you want.