Too many players, not enough DM's. I had to run a table with SIXTEEN PLAYERS. I invoked the caller protocol for the first time ever or since. Actually, I think we broke the groups into two groups of eight and had one caller per group.
It was still insane, but a lot less than it could have been.
Wow. I'm downright amazed that a few people here actually tried this. Nobody I've ever known personally has ever paid the slightest bit of attention to the idea of a Caller. I'm sorta' glad to see that this concept really did get some use!
I've always just found it goofy. I mean, as the GM, I'm sitting right there, listening to my players. If Jen says that her thief is going to creep down the hallway, I don't really need Jeff to repeat to me that Jen's thief is going to creep down the hallway.
Plus, without a Caller, there's no excuse for you not communicating what you wanted to do. If you were standing in front of the proton torpedo rack when the warhead detonates, you can't blame it on the caller, who "must not have mentioned to the GM that you were moving away from the torpedos, even though you very clearly told the caller that", etc.
Yup. We started out using a caller and a mapper. It was in the DMG, so we figured it must be important. We soon ditched the caller, since when playing with just four people it wasn't really necessary.
Still, the idea has a lot of merit, and I've enforced it later when playing e.g. Mechwarrior with 12 players or running AD&D for 14 teenagers. With Mechwarrior and other military games it also has the advantage of simulating issues of rank and command. It's an RPG tool like any other, which fits some games and does nothing for other (most) games.
I guess we've used this, very, very informally. We'd never actually call it a Caller, but there have been many times in games that I've run or played in that one person tells the DM what everyone is doing. This is normally after a bit of discussion, and the DM has one person sum up what people are doing, rather than asking each player in turn, "and what are you doing now?"