I seldom sash my quilts. It's hard for me to explain why...I try to sense what the quilt needs. I don't put borders on all my quilts either.

Sashing is like framing a picture. It calls attention to each individual block. If this is what you are going for, then sashing is something for you to try. Sashing is also a good way to add size to a quilt without trying to do it all with the borders. Once again, it's personal preference.