"Hey, if we don't clear this room, do these guys come when you engage Blackheart?"
"Yes they do."
"You've seen them come?"
"No, but WoWWiki says..."
"So you don't really know that they'll all come."
He had me there. I'd never actually seen it. Ten seconds later, however, I did see it when he told the party to wait in Ambassador Hellmaw's room while he ran up and engaged the Inciter. Turns out that puts the whole party in combat even if they are hiding very far away, so I made use of my handy Astral Recall spell while everyone else died a gruesome but informative death.
This made me wonder: have you ever disregarded the various guides, sources and general body of common knowledge about an instance and gone in cold? Have you ever tried something just to see what happens for yourself? I don't think we should run around seeing what that level with the skull on it does all the time, but as long as everyone in the party is okay with it, sometimes it's fun to experiment in game. It's like Mister Wizard, only he usually didn't end up having to run back to his body afterwards. Usually.