Don't forget that at some airports like O'hare that they don't sometimes even use ramp agents in certain cases when the plane pulls up to the gate. The new automated parking guidance system tells a pilot how far they need to drive in and left/right by the automated signs attached to the terminal. Backing up they wouldn't be able to see these signs. Majority of time it is used when there is weather or ramp agents are backed up but still the future of what will probably come of aircraft parking as technology evolves and labor costs are cut.