Modern cars are expected to produce power in an instant. What becomes of that power is up to the engine and performance components within to dictate. A differential is one of the components that takes the power that is given to it and finds a way to use it to the driver's advantage. In fact, a differential takes the energy that is sent to it from the engine and splits it up. Depending on your drivetrain, four-wheel or all-wheel drive, more than one differential may be necessary.
In fact, a differential changes the speed at which each wheel turns. While this may not seem like a great feat, it is quite an accomplishment when dealing with immense amounts of power. Not only do differentials decide where energy goes, but they also work to preserve energy to be used accordingly. That being said, a differential is a very important part of any auto.