Between action and cut a million things can go wrong. And if something does, you can always just cut to something in the editing room. Most of the time. "Doing it in one" is about the bravest choice a filmmaker can make. Without shooting coverage you are leaving yourself zero options in post production. You have to get the vision in your brain to happen in three dimensional space right there on the day. And you also have to hope that that initial vision is compelling and will flow with the rest film's rhythm.