Hey Terry,
no need to duplicate Dave’s pointers on how to edit racks and how to create rack states.
Just on the “useful scenarios for using rack states”: it helps if you think of racks as preset-based 19’’ expanders in your setup: you create rack states as you would create presets on your hardware synths. For any song, you just select the synths you want to use (i.e. racks) and connect them to your keyboard using routes and mix the levels of your selected synths using individual rack levels.
I have a couple of standard racks (piano rack, e-piano rack, organ rack, synth rack, guitar amp rack, …) that I use for my songs. Each of them has some pre-configured sounds (standard piano, ballad piano, lead piano, rock piano, honky tonk piano, … for the piano rack, rock organ, blues organ, ballad organ, soul organ for my organ rack, etc).
My song-specific setups are normally a combination of presets from these racks in a layered or split setup. I do a static mix of these sounds’ volumes using the rack level setting (per song state - activated in “state behavior”), plus the option of dynamic volume control via pedal or slider, using volume plug-ins within the racks that I control via MIDI commands sent to the racks.
So racks help me keeping my setup organized and my sounds consistent between songs by re-using patches, still allowing me a lot of song-specific flexibility.
Hope this helps!
Cheers,
Torsten