We wanted to make sure that those of you who work on a Mac laptop with an external display know that you can close your laptop’s screen and keep working. Apple calls this closed-clamshell or closed-display mode.
Of course, it requires that you connect an external keyboard and mouse or trackpad, via either USB or Bluetooth, and the laptop should be connected to power as well. Apple also recommends putting the Mac to sleep before disconnecting the external display. Why would you want to use closed-display mode? Mostly to conserve desk space when you have another preferred keyboard and pointing device, although it might also help graphics performance by allowing the Mac to focus on driving only the external display. There are lots of stands that hold a MacBook in a vertical orientation so it takes up less desk space.