This is a training mode designed to assist a total beginner learning to hover.
It might also be used by a more advanced pilot learning to hover "nose in".
To be most useful, you should also enable turbulence and/or gusty wind.
This mode locks the position of the helicopter at an eye level point, directly in front of the pilot.
The heli can roll, pitch, and yaw. But it cannot move in any direction.
The only way to exit this mode, is a simulator reset. Press space bar, or use the menu command Simulator->Reset.