This is one of the neatest features of these cameras! I have C1 set to what I call the Ansel Adams effect: b&w, 100 ISO, f8, hi contrast with the red filter. So, when I want to switch to a monotone quickly, I can do it by dialing C1. Secondly, all the settings can be changed easily, so if f8 isn't enough, I can make the change easily. Same with ISO or any of the others settings.
I have C2 set the same way but with the Sepia tone.
I haven't yet decided what to do with C3 on this one, but on my MkII, had that set to a long dof aperture, once again so I could select that set-up quickly when I spotted a bird in flight or other dritter moving in the woods and had no choice but to try a quick wing shot.
The great thing about this feature is that you can set the "C"s to anything you think you might need at a moment's notice, and without thinking thru all the seperate settings. They're pre-sets, there for you whenever you need them.