[Yoda]

#3 Power Accumulator
Not really understand this for sure, but what is this really? The roll of left arm/hand/club from p4 to p7, or is it the angle between left arm and clubshaft (which I find the same as #2 PA in practical terms)?

It's a "power" contributor (accumulator) yes, but any other benefit/consequence of mainly relying and making the most out of this in a swing?

And how?

The #3 Power Accumulator is formed by placing the Clubshaft under the heel of the Left Hand with the Left Wrist in a Level condition (upper left forearm and first knuckle of left hand forefinger in-line). In this condition, Left Hand Turn and Roll produces Rotational Power.

When the Left Wrist is Cocked beyond Level, the Swing Radius is shortened. Its return to Level -- and finally, Uncocked -- creates Velocity Power, totally independent of Rotational Power.

When Left Wristcock Power is employed, the Residual Velocity (of the Uncocking Left Wrist) is Transferred into Impact by the Level Left Wrist Roll. Hence, the designation of #3 as Transfer Power.