The servo booster was specifically developed for vehicles where the controller/receiver only outputs 6V, but the servo is designed for a higher voltage. This is often the case with Traxxas models, for example.
It enables faster response speed of servo motors, resulting in noticeably better control and agility of the vehicle. It is simply installed between the receiver and the servo, and converts the existing BEC voltage to 7.2V or 8.4V. This is an essential upgrade for RC car enthusiasts who desire better performance and control of their vehicles.
It is recommended to use the servo booster for models up to a maximum scale of 1/8.