ctrl + # is quite unspecific ... in-fact, its almost as generic as the pause button on your keyboard. In most games, tactical, strategy, or RTS -where you have alot of units milling about, you can select a certain number of units, and create a ctrl group based upon a number. Once you have made the ctrl group, you can select it merely by clicking on the number.
I used to use such for civ and FFH by separating the casters, seige weapons, fodder units, and heroes in a single stack, so that I can access things quickly. The main difference in ctrl groups is how intricate the system is, and if a single unit can exist in more than one ctrl group.
My personal favorite is when you can have any one unit be part of any number of ctrl groups at the same time ... mainly just to cover confusing results due to misclicks, although also included is the fact of quickly selecting a piece of the army, and then quickly selecting ALL of the army. In such a way, if you absolutely had to, you could order ALL of the units to do something in-between giving specialized orders to specific ctrl groups within the army. I believe the game I used this the most in was Dawn of War, although it was some-what useful in Total War games, and would be nice in Civ4's FFH.
Now however, the ability for ctrl groups is at least temporarily disabled, which slows down my game to an extent, although its merely an adaptation, like when Multiplayer games used to be exclusively Advanced start OCC, and then recently when we took an RP direction (even if it isn't always true to form ... mainly due to the same reasons why there is no world peace
) ... on that topic I think a separation of Lore-based games, and FFA games might be necessary, as well as perhaps the grey area of "Hybrid RP".