Funny enough, I was watching a video online last night of a Chinese master woodworker making a frame (bow) saw – the teeth on that blade were pretty fine and he set the teeth in exactly the same way. I’ve never seen that done before except on large saws used for cutting rough firewood. Larry has the correct answer as that third unset tooth acts as a raker to help extract the saw dust easier. I would think if you already like the way the saw cuts you could leave it that way when you go to set it. I could be completely off base here but it seems to reset all of the teeth alternating in the normal way would be considerable work. Maybe if you left the saw set as is for a few sharpenings the the teeth and set will wear down enough that they could then be set in the typical alternating pattern we all know? Good luck – it seems there is always something new we need to learn and why most of us love our woodworking as it keeps us coming back for more.