A SID machine foot is especially designed to stitch just to the right of your seam, so that you are not sewing on top of your piecing stitches. Also, it is recommended that you use the smallest zig zag stitch, rather than a straight stitch. Without the SID foot, it is virtually impossible to stitch anywhere except on the original stitches and hard to sew as straight as I want. When using a SID foot, the stitching is very close to but not precisely on the seam, so it looks good.