Mission Control was a feature added in Mac OS X Lion as an upgrade to the Exposé feature that was introduced in 10.3 Panther. It was done to accommodate Lion’s full screen apps. It simply brings forth every single open app in one screen. All the full screen apps, along with the Desktop workspaces and the Dashboard are lined on the top of the screen and the closest Desktop apps occupy the major portion of the rest. Exposé now only exists as a vestige that can be invoked on a per app basis by adjusting the option in the trackpad settings.