Level up: VIEWS!
With only eight layouts, and the possible desire of having different layouts on different controllers, you might imagine that you're going to run out of layouts. Not so fast... The new VIEWS feature multiplies the usefulness of your layouts. Think of a View like a WINDOW on the layout. A 12-switch layout can be broken into FOUR views on the FM3 or TWO views on an FC-6.
For example, Layout 2 "SCENES" on the FM3 begins by showing three buttons for Scenes 1, 2, and 3. When you press and hold the right switch, this advances to the next View, showing Scenes 4, 5, and 6. (And so on... Press and hold the Left switch for the previous View).
So, instead of "wasting" three layouts to grant access to eight scenes on the FM3, we can do it with just ONE layout on the FM3 thanks to the various "View" functions.
As you might hope, one FC can also change the VIEW on another. And this can be done with or without a layout changes. So, in effect, with not too much work, you can create one layout that spans the FM3 and a single FC-6. In general, I think most of us early adopters have found that this isn't as exciting or useful as some of the other options I described above.
See page 74 of the FM3 Owner's Manual for an introduction to Views on the FM3.