I enjoy some of the fancier buffets in Las Vegas and a few other places (there's a great one at the Palace Hotel in San Francisco). It's an opportunity to try a whole bunch of different foods that you wouldn't normally get a chance to eat.  A pizza buffet, on the other hand, is just pizza. It's just a chance to eat more pizza. And since all the pizza one can sensibly eat is already only a few bucks' worth of pizza, you're in for a world of gastric trauma.