Most of my backings are pieced, to take advantage of leftover fabrics from the projects. I cut or rip depending on the project. My favorite thing to do is use the serger to serge large pieces together. They make nice, uniform seams for the back, and they have not created any problems when I quilt on my frame. Also, I leave the selvages alone if they are on the outside edges, and they will be cut off anyway during the squaring off.