It enables you to create a passcode so whenever you switch the remote controller on. you would need to enter your chosen password, I guess in an atttempt to prevent an Air 4s for example from being flown and used when in the wrong hands.
However, if you forget the passcode it will reset the controller meaning you would need to relink it to the drone and apply all expo / gain settings again. Loss of video and screen recordings that are saved to internal storage of the rc.
You can disable the need to have a screen lock password though in the security settings in the rc.
In the update, there is also an additional flight location on the DJI Simulator called sunny island and fixes bugs in the simulator such as stick control smoothness.