Echoing doesn't mean stitching beside the seam. It's stitching beside another line of quilting. For instance you might stitch around an applique flower, then stitch again roughly the same distance from the first line of stitching, and repeat as many times as you like.
To answer the question though, you can quilt on both sides of the seam if you like, or only one side, or even make a lovely wavy line that crosses the seam.