What I know about LSD's would fill a thimble but in my research and thinking about using an LSD with the XDrive system is that the advantage for me is twofold:
First, using any type of limited slip will either eliminate or reduce the need for the traction control to engage the brakes to optimize traction except possibly in the most extreme cases under high power or unstable conditions. To me, this is the proper way to get power to the ground (without using the braking system to reduce/eliminate wheel spin to optimize traction). Ultimately, we're trying to make the car as fast and smooth as possible. Applying the brakes while the wheels are under load is an great way to solve the problem of not having a limited slip, but seems far from ideal. A secondary benefit of not engaging the traction control system would be that your braking system (at least the rears) would have less stress and wear, particularly at the track !
Secondly, if using a clutch type (Salisbury) the LSD can be built either 1.5 or 2 meaning that on deceleration, the clutch packs engage both wheels to provide engine braking and in my experience, tend to stabilize the chassis, most particularly when the chassis is unsettled (off camber, etc).
Also, I read somewhere that Porsche uses LSDs in their AWD systems.
I would love to hear others opinions and experiences as I plan to get a Dan Fitzgerald built unit (I have one in my E36 M3 and it is awesome).
