This presser foot is used for sewing blind hem stitches, which are sewn along the hems of pants and skirts to be invisible from the right side of the fabric.

By sewing with the fabric fold aligned on the guide of this presser foot, only a few threads of the fabric will be uniformly caught in the stitch.
Adjust the needle entry point or guide position according to the fabric before sewing.
You can also use this presser foot as a guide when changing the needle position for hem stitching in a straight line.