The main purpose of the vorpX desktop viewer is displaying the desktop, e.g. as a launchpad for playing games with vorpX without having to take off the headset in between game sessions. Besides that you can of course use it for any other task you consider it useful for, like watching SBS (and even spherical VR) movies or playing games with built-in SBS 3D support. Although in the latter case for various reasons it makes more sense to create a dedicated profile based on the ‘SBS 3D Base’ profile instead of using the desktop viewer.
Hope that helps.