viz. manual:

Onboard VGA
Enables or disables the onboard VGA function.
Enable If No Ext PEG
Activates the onboard VGA only if no PCI Express VGA card is installed. (Default)
Always Enable
Always activates the onboard VGA, whether or not a PCI Express card is installed. If you wish to
set up a dual view configuration, set this item to Always Enable.