Although Electronic Stability Control can be activated in a variety of driving scenarios, it is most useful during sudden swerves. For example, if you need to make a quick lane change to avoid a deer, ESC will help you move out of your lane. Crucially, it also helps you centre your vehicle after doing so. In addition, some situations require you to disengage ESC.
Traction control is a relatively simple technology compared to a full stability control package. It only prevents loss of traction at the drive wheels in cases where engine power exceeds the level of road surface grip. Although traction control systems use the same methods as stability control, their capabilities are much less. Stability control is just traction control with more vehicle education (computer programming) and better tools (a more powerful processor and more electronic sensors).
If you are one of the small percentage of people who take their cars to a race track, you are likely to turn traction control off as soon as you arrive and leave it off until you leave, looking for less interference and the ability to balance the car at its limit for better lap times and more Clarkson-like lairism. That's exactly what your traction and stability control systems do every time you get behind the wheel: be better than you in tricky situations, so it's never a good idea to turn off traction control on the road. Electronic stability control works in conjunction with a vehicle's anti-lock braking system (ABS), traction control and electronic power steering system. If you read car magazines, or watch Top Gear, turning off traction control is a sort of manly right, like having vomit come out of your nose, but in real life you might wonder why the button to do it is included.
Of all the optional safety equipment to look for in used cars, electronic stability control is the most important. So much so that grateful governments have made it illegal to sell new cars without stability control systems as standard. The only data the traction control ECU obtains about the car is how fast it is going and how fast the wheels are spinning. These seem like fairly simple parameters, but the way the stability control programmes work is quite extraordinary.
If the two don't match, the system applies the brakes on each wheel (as well as the engine controls, if necessary) to align the vehicle's path with the driver's intention. Off-road oriented vehicles that offer different terrain modes adapt the level of stability control intervention in each mode to suit different terrain, so it is best to set this mode to match the terrain to be driven over. Stability control works on the assumption that traction is best, always, and that the car should go where the driver intends it to go.