Here goes:-
Imagine you have a pencil with 2 cotton reels on each end. When going in a straight line both cotton reels rotate at the same speed. But when on a curve the reel on the outside needs to rotate faster than the inner reel otherwise it will just be slipping over the surface and not gripping.
The LSD in a car sends the driven power proportionally to the wheels with more going to the wheel that needs to rotate a greater distance. The drawback of having a Slip Diff fitted is that when one wheel has no grip and spins all of the power goes to this wheel. It is something you'll notice if you have one wheel in snow or mud and the other on a grippy surface leaving you effectively stuck. On a fast road you can get a sharper turning circle and put down more power if you modrate the rate of power going to each wheel. An LSD is exactly that and is usually specified as a ratio. For drifting you need a locking diff which encourages the back to slide over the road.
On a track or road the LSD will make a big difference to lap times and cornering speeds especially in low grip conditions like wet roads or when you are really hammering the engine. In a road test the Megane Sport beat loads of other hot hatches pretty much because it has a LSD fitted.
Audi provide a semi locking diff which gives the best of both worlds in pretty much all driving conditions.
Hope that helps a little. Now to turn this little lot into an article for the main site.... (Feel free to add any other points or correct me where I'm straying from reality!)
Thanks
