The 910 user guide has a good explanation for this ... pasting from page 4
Here is the link you can get the doc from (http://www.golfweb.lt/wp-content/uploads/2010/11/Titleist-910-user-guide.pdf)
Notes on face angle
Golfers will react differently to changes in face angle.
Some will square the face at impact and alter the loft.
-The head will have more loft when squared at impact if you start with a closed face angle.
-The head will have less loft when squared at impact if you start with an open face angle.
Some will maintain the club's static face angle and the resulting change in face angle will
-A closed face angle will result in left ball flight.
-An open face angle will result in right ball flight.
Some golfers will make a combination of these adjustments.
The golfer's ability to consistently return the club face at impact has a greater effect on
directional control than the face angle setting.
Ultimately, the golfer's ball flight will be your best source of
guidance regarding performance.