Using Only an External Monitor with a MacBook Air or Pro? This question Use Only External Display With Macbook asks how to use an external display with a Macbook  in clamshell/closed mode with attached peripherals such as external keyboard and mouse.

I would like to know how to use a Macbook (Air or Pro), in its own right (without the use of attached external keyboard and mouse peripherals) that is attached to an external monitor.

On Windows, you can right-click the desktop and select an option to output only to an external display. 

In OS X, I believe things to be slightly more complicated, therefore would like to know the precise steps needed to achieve this and indeed once finished with the external display, how to go back and use my Macbook as normal ?
Set the boot-args NVRAM variable to iog-0x0

sudo nvram boot-args=iog=0x0


and restart to apply the changes.

It restores the pre-10.7 clamshell mode behavior where the internal display does not turn back on after you open the lid of a laptop. The laptop will also go to sleep when you close the lid even when an external display is connected.

To undo the changes, run sudo nvram -d boot-args and restart.