The presser foot puts pressure on the fabric and keeps it in front of the needle, while the feed dogs pop up at every stitch and pull the fabric through. They can work against each other if there is too much top pressure so that when you have two pieces of fabric the same size, the bottom one goes through faster than the top one. Once you find the correct combination of pressure foot and tension for your piecing, all is good.
The walking foot has its own 'push' system so the thick sandwich feeds evenly and doesn't get stuck in front of the foot.
Some FMQ 'darning' feet like the one for my Janome do not hop up and down but can be adjusted to glide across the fabric at the right height so not to bind. It doesn't matter what the presser foot dial is set at.