There are probably several uses for this capability which I stumbled on a while ago. It works on iPhones too. It does not work on Windows. Plug your iPad/iPhone into your Mac, then start Quicktime Player. From the File menu select "New Movie Recording". Next to the "record" button there is an inverted "V". Click on that, and select your iDevice from the available options. Select the sound source. (Do you want the sound from the iDevice, or do you want to narrate it?) Select the recording quality. Click the "Record" button, and the Mac will record the iDevice screen. Press the "Record" button once again to stop recording. Handy if you want to create instructions for using an app etc.