the RCC is used to give the unit real time mapping of the planets surface, to allow it to find a better route. i.e. Without the RCC there is nothing to relay to the unit the topography. instead the unit has to work out the best route from what its sensors can pick up.
With RCC, the unit can plan its complete, most efficient route
Without RCC the unit has to plan its route as it comes to obstacles, just knowing the co-ords it needs to get to.
In enemy confrontations, the RCC acts as the skirish command center as well as having more power to compile all the data given to it by multiple vechiles. If the units had no RCC they would have to compile the data themselves/ between them (perhaps not enough computing power to compile the data, perhaps resulting in less informed decisions made by the units AI, due to lack of complete information?)