The advantage?
So you don't have to keep switching from the window, to A-SMGCS (GMR), to EFPS (electronic strips), and back again.
So you could perhaps have a visual indication through colour or symbol to represent confirmation that a pushback manoeuvre had begun, especially if the aircraft is parked end on to you, or perhaps round the back in the old Sierras, or at the bottom of the old Victors, which you can't see from the tower.
So you could see each aircraft's target take off time as you look out of the window to help you decide who gives way to whom, instead of looking at your strips.
So you can see aircraft type of something nearly two miles away in the dark as you're giving a conditional clearance on it to someone else withouit having to look down at your strips.
So you could have a visual indication of the aircraft being ready for taxi (having received such a request by data link) without the aircraft actually calling up on the R/T.
So you could see the position of aircraft beneath you, under the floor of the VCR, and check relative speeds, which is not so easy on A-SMGCS.
Apologies for the lack of order of those, that's just off the top of my head in a few minutes.
All those seem useful to me.