Years ago I used cotton sheets for both sashing and backings. I have gotten away from this practice. I guess as my stash grew I had more fabrics that were colorful or had a similar weave to choose from that I no longer felt the need to use sheets. In many instances I want the sashing to match the backing. Not always but many time I want to match the colors. The solids I use now are usually good quilting quality fabrics. I think it comes down to preference IMHO. The quilt in my Avatar is backed with a sheet.