This is how I use a satin presser foot to assist in lining up fabric for topstitching.
Satin presser feet have a grove or channel under them for allow bulky stitching to pass under easily.
There is a very good edge on the underside of this foot to line up against edges to help align for topstitching.
The grove/channel also is terrific for aligning a serged seam it fit in the channel spot on. There are also different sizes of satin feet. With grooves or channels from about ¼” to ½” wide.