I use whatever fits the quilt I am making best, sometimes its extra wide, sometimes its scappy sometimes its normal width joined once or twice depending on width of quilt. I don't have any strict rules, I just look at my finsihed quilt and then decide. The only time I bought the backing at the same time I bought material I ended up not using it as I didn't think it went well with my design on the front, just go with the flow and what suits you best at the time.