This setting is to provide better picture performance if user’s screen are mostly dark scenes. If no special needs(ex: playing shooting games in dark scenes), it is suggested to turn off.
Several ViewSonic LCD panels support both Landscape and Portrait modes. If your LCD panel supports this feature, you can switch modes by turning the screen as shown in the diagram below. To change the image on the Windows Desktop, follow instructions below: Open the Start menu and click "Control Panel." Click "Adjust Screen Resolution"...