If you happen to come across a small option named as Automatic Graphics Switching on your MacBook Pro, then it simply means that the latter is equipped with dual graphics cards. The Automatic Graphics Switching option is enabled by default and its main purpose is to adjust graphics performance on your MacBook Pro based on your current requirements.
Thus a MacBook Pro can automatically switch the higher performance (discrete) graphic cards for graphic intensive tasks (gaming, video editing, mirroring your Mac Book on a TV screen...) and back to the lower performance one (integrated graphics card) for a basic use (web browsing, document editing...), which in the process can help to extend the battery usage.
Why and when you should disable Automatic Graphics Switching?
Automatic Graphics Switching seems to be a great feature, so why you should disable it? Well, some apps have the ability to forcefully and unnecessarily enable the high performance graphics card and thus deplete your battery life.
Manage your graphics cards with gfxCardStatus
gfxCardStatus is free and open-source application that installs in the Menu Bar of Mac OS X (10.7 or later). It allows you to check which apps can force the activation of the discrete graphics card and manage the graphic performance of your MacBook Pro, three options are available:
Dynamic Switching - Enable the automatic graphics switching
Integrated Only - Enforce the use of the low performance integrated graphics card (incompatible with certain apps and won't work when your Mac is connected to an external monitor).
Discrete Only - Enforce the use of the high performance discrete graphics card. The same result can be achieved by going to System Preferences > Energy Saver and clearing the Automatic Graphics Switching checkbox.