Layouts are second level of categorization for controller maps. Layouts are specific to each controller type and are not shared as Map Categories are.
One possible use of a layout would be to have alternate map layouts for a controller. For example, you may have several pre-defined alternate controller layouts such as: Default, Inverted, Leftie, Classic, etc. You could choose to load a specific layout based on the player's choice.
Layouts could also be used as simply another categorization level. For example, for a shared controller such as the keyboard, it may be useful to have specific layouts for each player. Your Map Categories could be Default, System, Menu, Infantry, Vehicle, etc. to organize your maps by game mode, while your layouts could be System, Player0, Player1, Player2, etc., to further organize your maps by player.
For any controller type, only one controller map may exist in a specific category and layout.
To be clear, a Layout simply provides a way to retrieve a particular Controller Map in a particular Map Category. All modification, enabling/disabling, and other processes are done on the Controller Map, not the Layout. You could think of a Layout as sort of a tag -- it helps you get the Controller Map you want to work with in the right Map Category. To learn about working with Controller Maps, see the Controller Maps page.
Creating and Editing Layouts: