Which doesn't happen much, but here's a video in question:
Unfortunately, Shawn still works on the 'old ball flight laws' instead of the new ball flight laws that were 'discovered' by Dr. Theodore Jorgenson when he coined the term 'D-Plane' and are backed up by Trackman research and observation.
In the video, Clement states that the club path is responsible for the initial direction and the face angle is responsible for the curvature (Shawn says 'spin'). He goes with the Nicklaus method of working the ball by aiming the clubface at address as to where you want the ball to end up and aiming the body where you want the ball to start. You then swing along the same line as your body is directed with the clubface square to the target and then you can draw or fade the ball.
The big question is, why does this work?
Well, face angle at impact is mainly responsible for initial direction. Initial direction is attributed to about 85% due to the face angle at impact. The other 15% is clubpath.
So let's say you want to hit a fade and you use the 'Nicklaus Method' and aim the face square to the flag and open the stance and swing along the body. If the face angle is square to the target, the ball will want to start out straight at the target, but the 15% of the clubpath will start it out to the left (for right handed golfers). And if the path is outside-to-in, with relation to the clubface at impact, then the ball will fade (or slice). The problem is that golfers tend to over-do the curvature with this method.
One of the big reasons why is that it's far tougher to control the clubface in the golf swing than it is to control the path. I've talked to some people who own Trackman (some are non-teachers) and the general consensus is that people who use Trackman have a wide variance in face angles and a much smaller variance in paths. Meaning, a golfer can get up to Trackman and there's a decent chance they could have a very closed clubface at impact on one swing, then a very open face on the next swing, then a slightly open on the next, then a very closed on the next, etc. But with the path, if a golfer comes down outside-to-in on one swing, they are likely to come down outside-to-in on the majority of their swings. Better ballstrikers are almost always better because they control the clubface better.
So, with a square face at address, your risking an open face at impact which causes a big block fade/slice. Or even if your face is square, there's a decent chance you can start out too straight at the target and curve to the right of the intended target.
This is big news for most golfers, but I really feel it's big for the golfer that can struggle with the snap hooks. In the past, it was often thought that the snap hooks were the result of a very inside-to-out path (although that doesn't help). But the real cause of a snap hook is a closed clubface at impact. You can't hit a duck hook with an open face at impact. You can still hit a big roundhouse hook, but you can't hit one that starts left and low to the ground and hooks.
Usually the hooks are more related to grip issues. But they can also be a result of 'hanging and flipping' or for whatever reason getting the face closed in the backswing.
My biggest suggestion for somebody reading this online is to get a video of your swing and from the Face On view, stop the swing at the top. Here's a pretty good pic of Tiger and his square clubface at the top.
Notice how you can see the grooves of the clubface from this view. If you can't see those grooves in your golf swing, then you have a very closed clubface. Again, this is important for those who struggle with duck hooks. A slicer may want to have more of a closed clubface.
From the DTL view, the clubface should be on the same angle as the lead forearm at the top of the swing. Check out Rory McIlroy.
For the duck hook problem golfer, I actually prefer the Face On view because sometimes it's difficult to tell if the face is in line with the lead forearm from the DTL view.
If you can't see the grooves from the face on view or the face is pointing at the sky from the DTL view, then you may have a takeaway problem as well as a grip problem.
But for a basic understanding of D-Plane and the ball flight laws, refer to this D-Plane pic by Brian Manzella