The Traction Control System (TCS) is always on by default and pressing the TCS button temporarily deactivates it. When the button is pressed, a warning in the instrument cluster should indicate" TCS OFF". It will remain OFF until the button is pressed again or until the next time the engine is turned and restarted.
The only reason I know of to deactivacte TCS is when the vehicle is stuck and you are attempting to free it. If TCS is active, it will not allow excessive wheelspin that might be necessary to work the vehicle free.
When the TCS light appears during regular driving, it means that the system detected loss of traction and intervened to improve the situation. A brief reduction in power may also be felt at the same time.