A Setting that will, whilst a camera is activated and the left mouse button is down, display a wire frame scene in the 3D view. This is designed to improve performance whilst the camera is moving.
If this is set, when the user activates any of the viewing cameras - Walk, Orbit, Pan and Zoom - in the 3D view, and holds the left mouse button down, any faces displayed will be turned off and edge display will be turned on in visible models whilst the left mouse button is held. Once released, the scene will revert to its previous setting, although the camera will naturally be re-positioned.