Indeed, how anyone can not know what a LSD is...
anyway, with 400+bhp and RWD it would be most certainly very beneficial on wet slippery B roads -- or any road, if you don't know what they are you need to drive a car that has one - my Subaru has a torsen unit which is probably the best mechanical type one you can get, the transfer of power between wheels is pretty instantaneous which means its great for changing road conditions. It is rather surprising that the Jag does not have one, I am just a bit weary as going from a Subaru to a RWD monster can be quite the shock