A core difference between trying to 'keep the left arm straight' and extensor action (using the right arm to extend the left) is Rhythm, Rhythm, Rhythm!
The physics involved help the right side 'support' impact at exactly the right time - with the proper rate of clubface closing/motion - the proper amount of rotation. This GREATLY aids in consistency and supports full BALANCE, making it dramatically simpler to maintain. As another benefit, this all adds up to the 'heavy', 'smooth' motion feeling.
Not to mention the ability to maintain a flat lead wrist is just another, important BONUS
Percy Boomer understood this well.
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"Support the On Plane Swinging Force in Balance"
"we have no friends, we have no enemies, we have only teachers"
Simplicity buffs, see 5-0, 1-L, 2-0 A and B 10-2-B, 4-D, 6B-1D,
6-B-3-0-1, 6-C-1, 6-E-2