[YodasLuke]

It is my understanding that the clubshaft should always remain on-plane when it is swinging through the impact zone (which I will loosely describe as being between the third parallel and fourth parallel) and I am under the impression that this rule applies equally to swingers versus hitters.

The orbit that the clubhead will transcribe during its passage through the impact zone will be circular, and the size of the circular orbit must be related to the angle of the inclined plane - being smaller for a shallower inclined plane (eg. elbow plane), and larger for a steeper inclined plane (turned shoulder plane). The hands will also move inside more quickly if the circular orbit is smaller - eg. Hogan's swing where his clubshaft is slightly below the elbow plane (closer to the hand plane) during its passage through the impact zone - and that it is not dependent on whether a golfer is a swinger or a hitter.

Do you agree, or disagree?

Jeff.

I have to disagree. I would say it almost exactly opposite. The Clubshaft should never remain on-plane when it is swinging through Impact. If the Clubshaft stayed on Plane, it would result in a shank. The club has a CG or CM, which is an imaginary line that extends from Sweet Spot through the #3 pressure point.
“2-F…
Regardless of where the Clubshaft and Clubhead are joined together, it always feels as if they are joined at the Sweet Spot – the longitudinal center of gravity, the line of the pull of Centrifugal Force. So there is a “Clubshaft” Plane and a “Sweet Spot,” or “Swing”, Plane. But herein, unless otherwise noted, “Plane Angle” and “Plane Line” always refer to the Center of Gravity application. Study 2-N. Except during Impact, the Clubshaft can travel on, or to- and – from, either Plane because the Clubshaft rotation must be around the Sweet Spot – not vice versa. So Clubhead “Feel” is Clubhead Lag Pressure (6-C) and is a Golfing Imperative. (2-0). If Lag Pressure is lost the Hands tend to start the hosel (instead of the Sweet Spot) toward Impact – that mysterious “Shank.” When in doubt, “Turn” the Clubface so both the Clubshaft and Sweet Spot will be on the same plane at Start Down. Both Planes always pass through the Lag Pressure Point. Study 6-C-2-A.”