Traction control is a has a very close connection from racing cars like F1 and others.
This is one of the latest tech that manufacturer put on road cars but originated from Race tracks.
The basic concept is, to allow more torque to transfer from the engine to the drive wheels to the tires on to the contact with the ground.
More wheel spin = lost of power.
So, if you can transfer the power lost to one wheel that is spinning to the one that has traction, your car will get off the starting line first......
So, if you turn off Traction Control, when one of your wheel hits sandy ground or water, you will feel that you lost drive instantanusly or in another word, it's dangerous under the condition that you need torque or power to get you our from a dangerous position....ie, high speed turning on a wet or ice surface..
http://www.autozine.org/technical_school/traction/tech_traction_other.htm#TC
Read more here.....