A higher differential ball is designed to have more continuation, due to the amount of track migration it is able to achieve. A Lower RG ball has more tendancies to 'roll-out' due to it being more centre heavy, it uses up energy quicker during the skid roll hook stage.
A typical higher performance ball of todays game (note i said TYPICAL) matches lower-rg properties, with high differential, to enable a larger hook (due to quicker revs, and more flare potential, matching with stronger coverstocks)
This enables a bowling ball to not only gain energy throughout the skid stage of the shot, but retain energy until break, due to the flare potential. It then is able to release not only the energy from the bowlers actions, but also the core generated inertia and continue through the pins.
Simple way to remember all this information? If all other variables are the same,
Low rg- early rolling, revs up quickly
High rg- late rolling, revs up later down the lane
How differential- less continuation and flare potential, generally less hook potential
High differential- more continuation and flare potential, generally more hook potential
And with everything to do with bowling, its all about matching up!
Good Luck!