Joco,
The regulator is used when you run either a Gas engine or glow engine and you want to use Lipos for your power. Since the nominal voltage per cell for these are 3.7v, there isn't a combination of number of cells per pack that would equate to 4.8v or 6.0v to work with our more common and older Rx's(Newer ones are now allowing 7.4v range). Also, since most gas engines do not incorporate a magneto (way of generating their own power for spark), they use an external battery pack for charging the coil. A couple of reasons to do this include the reduced electrical noise generated by a Magneto, and also the reduced weight of the components (flywheel, pickup coils, etc.)
Hope this helps,
Curtis