The whole idea of standing on an unstable surface to improve your footwork and balance is nothing new, of course; you can find any number of such drills from various instructors. But you don't often hear players say that they're doing these drills to improve their shoulder coil. (Note Paula's hashtags #thatshoulderturn and #thathipturn.)
The nice thing about this version of the drill is that it's a really cheap version. Many folks have (or know someone who has) extra bits of 2x4 laying out in the garage. And if not, a 2x4 is extremely cheap at a building supply store.
So here's yet another version of the balance drill you can add to your practice arsenal.