I have tried, on and off, with using banks. I tend to make many changes and since Nikon does not give you an option of returning to your original settings (without reloading them from a memory card), I continually screw up what I had. Although I am still trying to get to use the banks, I think I am now moving back to the fact that one bank is less complicated.
I could see another bank being just set up for someone who you want to hand your camera to and just use it as a point and shoot. My normal shooting style has back button focusing and that would be difficult to use if I asked my wife to take a picture.
Maybe someone will have the magic thoughts that could get me enthused about banks but currently I am not.
I can't help but wonder why Nikon doesn't make this easier by allowing you to save your settings and then if you wanted to make changes ask you to verify that the savings should be saved.
Since any setting changes are auto-saved into the active bank as you change them, I have gotten into the habit of manually resetting the camera back into MY default state for the bank at the end of the day/shoot so that the next time I pick up the camera, I will know what state it is in.
I, too, normally use the af-on button; but for my "snapshot" bank I have the focus set to shutter-button, just so I can hand the camera do someone else if needed.
Whether or not to use the banks mostly depends on how different your camera settings are for the different scenarios you shoot in.
---------+---------+---------+---------+ Joseph K Seattle, WA, USA