Good discussion! Sometimes I buy wide backing specifically for the quilt, usually if it is a Queen sized quilt. For smaller quilts I often use one of the fabrics from the front of the quilt. On a recent quilt, I pieced a good portion of the back, as I wanted to use of some of the coordinating fabric from the front of the quilt. (Plus it was fun!). For a recent baby quilt I used a prized flannel blanket that was my daughter's baby blanket as the backing for the quilt. Sometimes I buy fabric I fall in love with, but would not use in a pieced top. I guess it depends on each quilt, the size, and planned use.