because of the larger diameter of oversized disk brake rotors, you get more surface area. more surface area means the rotors cool faster which in turn makes for a powerful braking power. that is one of the reasons why they use big brakes in racing bikes and cars... these vehicles go faster that is why they need extra effort to stop.
but a light vehicle does not need big brakes. your brakes must be balanced to the weight of the vehicle or else, it's going to be hard to control when you're braking.