I found it a little strange too - but on a closer look, you can see the post dates reveal that an old thread has been "revived", and what you most likely have is a newbie asking advice.
To my mind it's a fair question and I have wondered about it myself - I recognise that an LSD will do nothing for you if you have a wheel up, but what about when you have both wheels down, in sand - you do have some traction. Yes, depending on the type of LSD, they wear rapidly, but quite a few manufacturers fit them to the rear of their larger 4WDs either standard or as an option - they must have some benefit.
Going off on a tangent - I recently picked up one of the smaller Mitsubishis - a Pajero Io (Pajero Pinin), it's about the size of a 5-dr SideKick - I have yet to figure out if does have an LSD which apparently was standard in some markets.