[12 piece bucket]

You would sweep the broom along the 'reverse plane board'.

Heres two things for starters...

Throwaway - If you sweep the board, you won't be throwing away the clubhead. It would come into impact like striking a match. Great for teaching people how to not have throwaway.

Plane - If you were to effectively sweep along the board you would have the flat part of bristles of the brush touching the board. You also learn to make this motion along a straight plane line. You wouldn't sweep the imaginary dust from the board with part of the bristles would you? This teaches that you have to be on 'a' plane angle as designated by the lie angle this is what Moe Norman describes as - 'being on the same height'.

Wouldn't that encourage "covering" the plane line and not tracing it?