Wrist is the most mobile joint in the whole human body. It can flex, extend, deviate and perform all possible combinations of these motions. When we add also the pronation and supination of forearms it appears that our hands can move in practically all directions. In view of this fact wrists can be seen as chains in between nunchaku sticks joining forearms and hands gripping the club, hence joining practically arms and the clubshaft. This notion is very important for those who believe in lack of conscious actions in this area of the body. Let us remind here the famous quote from Ben Hogan's '5 Lessons' book:
THE ACTION OF THE ARMS IS MOTIVATED BY THE MOVEMENTS OF THE BODY, AND THE HANDS CONSCIOUSLY DO NOTHING BUT MAINTAIN A FIRM GRIP ON THE CLUB.
Mr.Hogan was of course right, as almost always. But the biokinetical truth is more complex than that. Our wrists are capable to both deviate in both direction (cock/uncock) and flex in both direction (hinge/unhinge); moreover, there is a coupling between these action described in our 'Omnium Trium Perfectum' article, namely that the most usual movement of the wrist is one of dorsi flexion (extension) combined with radial deviation, and of palmar flexion combined with ulnar deviation. Pure palmar-dorsal flexion (flexion-extension) and radial-ulnar deviation are movements that rarely occur in a straight plane. It is like that because when we want to maximize ulnar deviation range we unintentionally bow the wrist which means we flex it palmarily; conversely, when we want to maximize radial deviation range our wrist becomes dorsally flexed. It should give us the picture that the axis of wrist deviation RoM is not parallel to pure deviation motions but is slanted from slight palmar flexion to slight dorsal flexion just as shown below (we shall call it "the Golden Axis"):
Please note what scientifists wrote (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3260558/) : "The earliest notation of the functional use of conjoined wrist motions is attributed to Fisk, who noted the association of wrist extension with radial deviation and wrist flexion with ulnar deviation “when someone is casting a fly, throwing a dart, or conducting an orchestra.” Palmer et al showed that many occupational activities, exemplified by hammer use, involved an arc of motion from radial deviation and wrist extension to ulnar deviation and wrist flexion. These investigators popularized the term dart thrower’s arc to describe this conjoined wrist motion. Indeed, nearly all sporting activities, including pitching, racquet sports, fly fishing, javelin throw, batting, and golf also use the dart-thrower’s arc of wrist motion."
The clubhead momentum created after the top during the downswing phase is huge (the head is relatively heavy because it is located at the end of a long shaft) not only ensuring a strong hit at the ball but also enough large to create balance problems of the whole body at the end of the swing. The lead wrist after impact bends at an angle (and not just purely radially deviates) which can be easily seen when we try to maximize its range of motion up which is totally in accordance with the slap-hinge release principles. Momentum vector is in line to the axis of maximum radial deviation enforced by the help of dorsi flexion. Further motion along the Golden Axis leads to absorb the momentum in the most effective way as the limit of the lead wrist's motion range is being reached in the most natural and neutral way possible -- no excessive or intentional supination/pronation of forearms which is equal to clubface stability, repeatability and consistency of strokes within the pattern. It even can be a primary goal to eliminate conscious pronation or supination; pronation and supination of forearms should occur totally unintentionally; the follow through without supination of the lead arm and pronation of the rear one requires to be preceeded by the slap-hinge release (or, at least, by some elements of the slap-hinge release, i.e. dorsal flexion of the lead wrist after impact) since without it the sweetspot would wander off plane or would require a very strong pivot and pure push release (not a good option for seniors and body-handicapperd golfers) or just an early swivel as in the heavily timing-dependent crossover release.
This is extremely important for draw patterns that require long flat spot and it is crucial to have stable clubface all the time there -- fades basing on slight OTT accross the ball have a very short flat spot, hence potential problems with clubface horizontal stability are minimal comparing to draws.