I don't have two flashes but would assume that both dump light until the exposure is met. You can have one flash six feet away lighting only one side of the victim and the main lighting the other. Once exposure is met, they kick off. Of course one side of the face will be over exposed compared to the other. Then you kick in a different ratio to fix the power to give a more pleasing look. Like I said though, I don't own two flashes and barely know how to handle one.