Dont you mean off mate? Its on all the time unless you chose to turn it off.
With it on you cant launch the car properly as it bogs it down, it also upsets the balance if you go into a corner and intend to get a bit of lift off action, the car kerbs that and pulls it back inline, not good if you were ready to have some fun.
Its more a safety aid should you be put in a position where you need to take evasive action of some kind. Under normal driving the system rarely comes into play.