I adjust the tension on the foot when I am sewing on thick fabrics. Use a large needle and lighten the pressure to make it easy to go through the fabric. There are a lot of benefits to changing the pressure in different applications. Sometimes if your fabric doesn't seem to be feeding quite properly and the stitches look short for the size you dialed in, tighten the pressure so the feed dogs and foot grab the fabric better.

Lightening the pressure also keeps the top fabric from bunching up in front of the foot which can result in sewing pleats. I lighten it so I can avoid having to put on the walking foot sometimes.

And as mentioned earlier, the instructions for many walking feet specify loosening the pressure while using them.

Thank you - that video was very helpful.

I reduce the pressure when the fabric seems to be bunching or dragging due to many seams coming together in one place. It helps the foot to glide over them easier.

Like many other screw based adjustment things "rightie tightie, leftie loosie". If you want more pressure, tighten it, less pressure, turn it back the other way. It doesn't need major adjustment often unless you are switching back and forth between piecing and quilting.

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.

Thank you for this. It has answered questions for me.