I seldom see the point in it as many people hang it on the wall and then have to put some sort of cabinet under it anyway to hold the cable box, DVD player and audio system. I just stand mine up on the audio/TV cabinet. Hanging it up will not save me any space and quite frankly some people do not mount them at eye level because they look funny at that height so you end up with neck aches looking up at the screen.
Of course if you are not going to put any furniture under the TV then it makes sense.