I pre-wash (except pre-cuts) because I have asthma and the chemicals in the dye trigger my asthma. This is really a problem when I iron the fabric if it isn't pre-washed. When I walk in the door with fabric, it goes right to the laundry room before it even sees my sewing room. If I'm using a pre-cut or kit, I open the window, use my inhaler, and iron as little as possible. I always use steam. It takes less pressure on the iron. I agree with everyone else, there are no rules. You'll find what works for you.