The listener represents the microphone position in the game so 3D sounds can be positioned in the speakers to mimic a real 3D environment. This is done by mapping the game objects' positional information into the listener's coordinates system. This coordinate system is defined by a position vector, as well as front and top orientation vectors. It is therefore necessary to keep the listener's positional information up to date, otherwise sounds will be rendered through the wrong speakers.
For more information on Listeners, refer to Integrating Listeners.