The neck/head system and its impact on a motion is, IMHO, very underestimated and overlooked. First, two VERY IMPORTANT facts:
- the head is really heavy; the weight of it amounts to ca. 7.5 % of the whole human body weight; moreover, it is the most distant part from the human body CoG (which is in navel area - for an adult man; for an adult woman - a bit lower, BTW) that makes head's motion impact on ANY CoG shift even bigger;
- the spine "goes into the head" not centrally from a geometrical point of view, but from the back; this fact not only makes it impossible to turn the head more than the shoulder lie in both directions (although the head can move in all possible directions), but also implies how the head should be turned in order to be in synch with the turn of the spine - it reminds more of an eccentric wheel motion; if your shoulders turn back your head should also turn back while keeping the neck still.
Since the golf swing motion relies on turning of the whole upper body back and forth, the head should turn perpendicularily to the spine turn. However, there is no limitation in its independent movement, because, as I said before, the head can be turned more than it is needed in a golf swing; it does not - why ? If there is no limitations ? The answer is very simple - because its movement is dependent on a human's most important sense - the sight. We are constucted the way that our senses (through our brains) are the bosses. We cannot lose the golf ball out of our sight (unless someone is specially trained to do it or can play a "blind" golf). This is the most overlooked aspect of all aspects that concerns the golf swing motion...and I mean it.
Back to the topic - the limitation is then equal to the maximum turn we can make while still keeping the ball in the range of our sight. But it is not everything - eyes (as ears) are instruments that appear in a pair. Moreover, if a pair happens in our body - one of the "member" has to be a dominant over the other...no matter if we are talking about senses but also about arms or legs. There are no ambidextrous persons - one can be close to ambidextrous, but never fully ambidextrous, especially when talking about senses that are subject to our DNA (in short).
Now imagine - a right-handed golfer with a dominant right eye vs. a right-handed golfer with a dominant left eye (BTW, it seldom happens that a right-handed man is a left eye dominant person that may say why only 1% of golfers are being told as supertalented persons). It becomes obvious how much better head turn and much better upper body CoG distribution happens when the head is more in synch with the upper body turn. Look at Hogan (who was reported as left-eye dominant right-handed person) and his head position at the top. Does it disturb in their full excellent upper body turn ? No ! Look at Moe Norman - he was obviously a right-eye dominant person and he had to lift his head a bit up when coming into the top, but his instinct never told him to go further with his backswing and avoid further "collision" between left shoulder and his chin ad to worsen the relation between head position and spine angle.
Therefore, let us say that the limitation is your sight range; I do believe that many golf swings are wrecked because golf teachers are very stubborn as regards the head and its position, especially in the downswing and impact phase. Should the head be before the ball at impact or THE DOMINANT EYE BEFORE THE IMPACT ? Mind you, the head weights a lot and every possible position that is not natural may bring more harm than good. Forcing the head to be entirely behind the ball makes it being out of position in relation to the spine and may bring flaws in ballstriking easily.
In view of the above, it seems very comprehensible, that it is useless to force our bodies to be in position of Hogan while we are right-eye dominant persons; it would sound odd, but the biokinetics answers that e.g. a S&T golf swing pattern may be better suited for such a person; moreover, we cannot forget about the impact of the head movement (or lack of it) on the whole movement of CoG of our bodies in a golf swing motion. The less it is turned back, the less mass moves back. The less mass moves back, the less the CoG shift at the end of backswing happens.
The choice is - either to risk to move less mass of the whole upper body back or to risk to move the head not in synch with the spine turn (which is practically equal to unnecessary spine angle deviations).
If we choose the first option, we shall end with a poorer shoulder turn, shorter backswing, less powerful swing, less coiling, smaller X-factor, etc., BUT WE SHALL REMAIN IN SYNCH WITH OUR SPINE'S MOTION. Of course, we will not be a Re-MAX LD champ, but our accuracy increase tremendously, IMHO.
A word more about the position of the head in relation to the neck. Note that every great ballstriker's upper spine (watching from a DTL view) is not rigid, they look as a bit hunchbacked at address, and never rigid. Why ? Because they did not force their heads to be in an unnatural position starting from the beginning. They "accepted" the fact that the head weights a lot (especially if one is bent over 30-35 degrees while swinging) and wanted to subdue their head's motion to the spine motion UNTIL THE DOMINANT EYE PREVAILS. They did not want to cheat the sight with a high head position and looking throught the nose.
Moreover, increasing the spine angle (commonly watchable during transition) is always linked to the drop of the head....not coincidentally - the head respondes to the spine angle change, that's why it drops down a bit. What is funny is that hadly anyone see the coexistence of losing the spine angle with the head position and counterbalancing with our tush part. The head is so heavy that any horizontal level change of its position when swinging (while being bent !) may cause us stand up (i.e. lose our tush line). Some of the reason for this common fault may be linked to incorrect head motion during the swing.
I wish there are more researches about the impact of eyedness on various motions in sports, especially rotary-type sports, as golf is...it may be more important if we all think.