It seems to play on the idea that lying down is more comfortable than being upright. Leg extension without one's weight over the pedals makes it difficult to develop power or deal with bumps. The neck position can be just as uncomfortable in reverse as cranking the head up off drops is. It can be hard to do a shoulder check. Like anything else it is a mater of trying it out, if your LBS has something for you to try, and seeing how you like it.