It's very effective keeping the FA announcing the position to remain in. Once they stop the repetition, people WILL look around either exposing themselves to danger OR the event is over and it's time to get out ASAP.
But it sure does make it difficult to take videos out the window.
I suspect some of the screamed repetition of brace brace over and over also serves to calm the nerves of the FA's giving them something to do other then contemplate their own mortality.