There are times when you want to hide stitches around the seams – a great example being when one quilts, occasionally you want the design to be a focus point rather than any top-stitching.
In this situation you will want to stitch in the ditch, in the well where two seams meet. A ditch quilting foot greatly eases the challenge of making these perfectly placed stitches; it has a metal guide down the centre that separates and spreads the seams.
You can also use this foot as a guide for top-stitching; use the centre guide to line your needle and fabric precisely.
Another name for this foot is the Edge Joining foot.