As I understand it:
TCS looks at the difference between front and rear wheel speeds and cuts power if it detects a loss of traction at the front - that is, front wheels overspeeding. It would come in if you overcooked a drag-race start from the traffic lights or if you push it too hard in a corner. If you get TCS cutting in on a dry road, you have hit the limit of adhesion for your tyre/suspension combination, and been saved from losing the plot in an embarassing way. If you feel you need more performance, look to your tyres and suspension, to get the power down.
If you switch off TCS you still have EDL which is part of the ABS system and can't be switched off. It mimics the function of a limited slip diff by braking the unloaded wheel (usually the one inside the curve) - without TCS, this will let you break traction with the outside wheel too, which usually leads to understeering into the scenery.
Outside of the racetrack, it is not considered polite to drive on the limit of adhesion, as you have no margin for error. If you find you are regularly provoking the TCS, and have already sorted the suspension and tyres, then take up circuit racing, where your accident is unlikely to hurt anybody else and full emergency facilities are close at hand.
The TCS has to be switched off when you have a puncture and use the spare. It's also confused by low-friction surfaces e.g. deep snow, mud, gravel.