Stay on the ball! This is another one that is often debated among teaching professionals (no shortage of such debates really), and slow-motion videos of touring pros are often used to emphasize the point that the head can and occasionally does move rearward in varying degrees during the backswings of many great players. (And yes, you can find videos of pros that illustrate a centered turn as well...far more these days than days of yore.)
But we've also heard the adage that we should "turn like you're standing in a barrel." While I think you'll find that there are no shortage of differences among professional golfing turns and pivots as they relate to the position of the head during the backswing and downswing, I believe that we amateurs benefit by staying as centered as possible. Why?
If you move off the ball during the backswing (i.e., your head shifts too far over towards your back foot), you've effectively moved the swing center backward from where you established it at address. In short, you've introduced unnecessary inconsistency into the swing. This means that the bottom of your swing arc has also moved backwards and will require timing to get it back to the right place consistently. Remember, pros can do all sorts of crazy things because of their talent--not necessarily because it's the right way. Also, you increase the chance that you'll sway (i.e., your weight will move to the outside of your back foot instead of staying on the inside where it should be).
Here's what you should try. Set up using the proper posture, grip, aim, and body alignment. With your shoulders properly squared to your knees and hips, your right shoulder should be noticeably lower than the left (assuming you play golf right-handed), and this will place your head slightly behind the ball using irons and wedges (the wider your stance and longer the club, the further your head will be behind the ball at setup).
Now, focus on the keeping the lower body stable and unmoving during the takeaway and backswing, as your shoulders turn and your weight turns into the inside of your back leg. The feeling you want is that the hips and knees stay parallel to your target line for as long as possible and only move in response to the shoulders turning back. Your head may move slightly to the right as a result, but it should stay relatively steady.
Achieving a centered pivot is possible when you recognize that the right hip does NOT move to the right at all during the takeaway: It moves straight back and even towards the body's center line in response to a proper shoulder turn, and the right leg stays angled towards the target (does not move towards a perpendicular-to-ground position). The right knee also stays bent. As a proper on-plane takeaway keeps the club head outside of the hands, the correct opposing move is for the right hip to move straight back. This thought should also keep you pivoting correctly.
Now simply unwind into your downswing and try to keep your head in the same place (or even moving slightly back) as your arms come through. One thing all pros do is to keep theirs heads behind the ball during the downswing. In some cases (especially with the longer clubs like driver), you will notice that the heads of professional players will sometimes even move further back (secondary spine tilt increases) as the arms come through. But that's only during the downswing and usually with longer clubs.
Strive to stay centered on your backswing pivot and behind the ball on the downswing and you'll gain consistency.
The classic teacher from the 1930s Percy Boomer coined the phrase "Turn in a barrel." Boomer recognized that turning around your body, rather than sliding your hips sideways, results in more consistency. It's difficult to hit it solid when you move off the ball on the backswing, because you have to move back to the ball the exact same amount to hit it flush. That takes more talent than most golfers have and more practice than they can afford.
"Turning while keeping your chest in place not only eliminates swaying and the likelihood of fat contact, it improves the quality of your rotation, because if you sway you can't turn. Ditch the sway and your backswing becomes 100 percent rotation."
The body needs to make a centered turn around your spine with limited up and down or side to side motion, thus creating an efficient coiling of the upper body and lower body.