I can't see any conceivable benefit to shooting the same shot 500 times in a row; I understand the point of drills and repetition, but focusing an entire day's practice on a single shot seems like overkill. I think by the time you've shot it 50 times, your mind is going to be losing focus and the additional shots aren't going to help with retention. The practice method which I see mentioned here most frequently has less to do with shooting individual shots over and over and more to do with finding certain drills that help focus and train a specific area of your game. I don't actually know many of them and I don't practice them (which is probably detrimental to my game), but it makes sense that focused drills are going to aid you more than learning very specific individual shots.
I think alot of it is personal preference as well. For me personally, shooting the exact same shot 500 times in succession would probably be enough to convince me never to pick up a cue again; my brain would not deal well with that level of repetition. For others, shooting the exact same shot time and again can help them achieve an intense focus. It all boils down to the individual and how they best learn (and retain). I would suggest finding some good drills to someone who was focusing on getting the most out of practice sessions, but there's something to be said for mixing it up and practicing individual shots or playing the ghost. The worst thing you can do is get too monotonous; it makes you want to not play.