Wow interesting discussion. Its clearly one based on point of view. From the guest's PoV, enjoying the event and all that means is paramount. From the pro's PoV, doing the best job they can is critical.
But what seems lost here is what the B&G want. Anybody bother to ask?
When interviewing for our wedding one photographer, the one we choose, asked us. He brought this very point up, saying he's willing to work either way. He explained how one style might produce better results, but that it might impede on the guest's enjoyment some. He also explained how the results *might* suffer slightly, but that the guests should feel free to do their thing... in other words, he was asking us if we wanted him to run the show, or if he was to take on the role of observer only.
He brought up and we discussed how to handle it if a guest was impeding his his ability and if we choose the former. Explained how this can sometimes be uncomfortable.
We ultimately chose a hybrid. There was clear time set aside for the pro, but most of the time he was to use his creativity and work with what the experience presented. He turned in some amazing results and nobody felt like he was trying to run the show.
So... why not ask, explain and communicate before the event? Maybe its best not to assume you know how the B&G want things done? Worked for us anyway...