The FC12 is awesome if you do kitchen sink presets. Also, coming from the MFC, I had a general layout memorized, and the FC12 helps keep me working with a very similar layout for my "perform" layout. You can get a massive amount of stuff done with the FC12 and external switches. For example:
My far right top & bottom switches are pretty much always Tap Tempo/Looper, FX Layout/Show Hold Functions. This leaves me with two rows of 5 switches to play around with. The tap/hold functions of my stand in switches are Looper Layout/Scene 8 (acoustic input) and Volume Boost/Delay Boost for now. Basically stuff I always want available but don't want to accidentally stomp in the heat of the moment.
Perform Layout: Has 5 scene switches on the bottom and my 5 most used effects on the top. The hold function of each effect switch toggles to Channel D, which I have reserved for special purposes. The hold function of each scene engages an effect similar to the switch above it. IOW, if the tap function for the top left button engages Delay 1, the hold function of that switch changes to Delay 1, Channel D, with the feedback/mix tied to an expression pedal. The hold function of the button underneath it engages Delay 2. Another example, the tap function of the 5th button is Drive 1, hold function changes to Drive 1, Channel D (fuzz pedal), and the hold function of the switch below it engages the Amp Boost.
More FX Layout: This "slides" my effects up. So the effects that were hidden as hold functions "under" my scene switches are moved to the top row where I can see their on/off status as well as access them by simply tapping. I have some lesser used scenes that move to the bottom row, and the hold functions of those switches access even lesser used effects.
Looper Layout: I slightly modified the default to have all my looping functions along the bottom with my 5 most used scenes along the top.
Preset Layout: I set this up with a bank size of 8, with buttons to Bank Up/Down by increments of 1 or 10 (tap or hold, respectively). This leaves 8 buttons to switch presets, and the hold functions change scenes. So basically I can audition presets and their various scenes through the preset layout. I have it set where it does NOT go back to the perform layout when a preset is selected, since I don't change presets that much.