I need to use mine if I want the stitching to be straight. The metal part of the foot goes into the seam line and the stitching is therefore just to the right of the actual seam stitches. Before I got the foot, I thought SID should be sewn right onto the existing stitches so I was confused when I first used it. I then did some on-line research, which said that my SID foot was behaving correctly and that sewing directly through the quilt seam stitches is not a good thing.