If you have a practical quarry design, it makes sense to extract exactly against that plan.
Over-digging can result in face stability issues, rough floors and excavation outside of extraction boundaries.
Under-digging can result in valuable material being left behind or too much material left on the floor (and who wants to pay to drill & blast it a second time).
A GPS Rover is definitely a step towards solving this problem, but a more effective way is to fit machine guidance to loading tools and dozers. This enables your operator see exactly where they are in relation to design and dig accordingly.