The following was taken from the internet discussion on Golf Tips.
Many wood (or metalwood) clubs appear to be "open" in the address position. This seeming phenomenon is caused by a number of things which create an optical illusion. The angle of the left eye to the clubface with the right eye to the clubface is about 2 degrees; also one eye usually has dominance over the other. Coupled with the fact that woods are usually placed slightly forward in the stance and some players have difficulty focusing on the shaft simultaneously to that of the clubface angle, it is not hard to see that this illusion does occur.
Should the club's face angle be open? That depends on your usual shot direction and shape and how much the face closes due to the flexibility of your shaft. Because the clubhead is traveling faster than any other point along the club and is accelerating coming into impact with the ball, the shaft normally flexes in a bowed-forward position. This flexing action causes the face of the club to close slightly.
If your typical swing technique returns the clubface to the ball in an open position and results in a push or slice, you don't want your club's face angle open. However, if your swing normally produces a hook, a slightly open face will compensate for your technique and reduce or eliminate the hook.
There is an inter-relationship between club path and face angle that must also be considered, but the easiest way to correct hooking and slicing tendencies is by adjusting the clubface angle to the degree that it produces the most desirable shot pattern considering the face angles relationship to club path.
A professional clubmaker can evaluate your present clubs and either adjust the face angles or recommend equipment that will straighten your shots.
FACE ANGLE is usually never considered a factor by most retail stores. In fact, if you asked an employee at your favorite retail or discount golf store "What is the face angle of this driver?", the most common response is to simply repeat the loft marked on the wood.
As stated above, face angle MUST be considered when fitting for the right wood. As an example... if you have a driver that shows a 10-degree loft, that may or may not be the effective loft at impact. To get a complete picture, you must factor in face angle! Here is the simple formula--although it may sound backwards at first. Loft PLUS closed/hooked face angle EQUALS effective loft at impact... likewise,
loft MINUS open/slice face angle EQUALS effective loft at impact. Therefore, if you are looking at a 10-degree driver and it has a face angle that is 2 degrees open, the effective loft at impact is 8 degrees! Quite a change! Now, who says face angle is not a factor to consider?
The professional clubmaker can make adjustments for draws/hooks or fades/slices by fitting you with a head that has a particular face angle... BUT, your professional clubmaker must always factor in the effective loft - is it too much or too little for your ability and desired flight path.
The article also states... "Because the clubhead is traveling faster than any other point along the club and is accelerating coming into impact with the ball, the shaft normally flexes in a bowed-forward position. This flexing action causes the face of the club to close slightly." Again, here is where your professional clubmaker is KEY! A properly fitted shaft - based in large part on your swing speed - will return to vertical at impact... and will not lag or lead the clubhead. This is why I measure swingspeed for woods and irons, then do a computer search for the proper shaft to meet your needs.
Shaft fitting is absolutely critical! All "stiff" shafts are not alike among the multitude of manufacturers... the same is true of all flexes. Many adjustments can then be made off that baseline... for example, given your desire to emphasize accuracy over distance or distance over accuracy, I can adjust the search parameters and get the results you desire!