You can see the hollowed out underside that was designed to allow a bead of satin stitching flow unimpeded. When you use these feet for normal sewing, this happens:
I hope this is seeable. As the needle pulls up, out of the fabric, it pulls the fabric up with it. That's because there is little or no downward support for the fabric. How that shows up as a problem can be seen here:
On the straight stitch, the knot isn't always in the center of the fabric and on the zig-zag, you can see the pucker. This is because the fabric is not properly supported under the foot.
In this picture:
You can see, when using the regular foot, whatever # or letter that happens to be for your machine, the straight stitch is perfect and the zig-zag did not pucker. Same thread, fabric and tension setting.
For full disclosure: Sewn on Shelley's B770 with Aurifil 50wt cotton, Sevenberries Cotton fabric, Organ HLx5 size 80/12 needle and all settings at default.