Performing stunts is not something that you would want to do, if you love your car, but, for the daredevils, they would do anything even if it means that it would endager their lives. They like the idea of tricking their body into feeling that they are in danger. The feeling produces adrenaline, which makes them stronger.
In this game, you need to do some stunts while on air to activate the booster. With the booster activated, you can cover more grounds much faster. Grab as many coins as you can because you can use it to upgrade your car.