There's a lot Stability control (ESC) can do and one of them is it can reduce engine power or operate the transmission to slow the vehicle down, like if it thinks the car is skidding. Due to the fact that stability control can be incompatible with high-performance driving, many vehicles have an override control which allows the system to be partially or fully deactivated. (from Wikipedia)
From the Equus manual: The ESC system is to stabilize the vehicle in cornering maneuvers. The ESC monitors your steering and driving. The ESC applies to a brake of an individual wheel and engage in the engine management system in order to stabilize the vehicle.
So in a racing situation you want both the Traction Control and ESC defeated and the tranny set to sport for the best performance this car offers.