If a
putter is face-balanced, then when it is balanced along the shaft, the face will point perpendicular to the ground. Straight up. The
theory behind face-balancing is that when you
stroke a
putt, you apply
force to the putter during the
downswing of the putt. If this force is applied anywhere other than directly behind the
center of mass of the putter, then a
torsional force will be exerted on the putter's face. The putter's face will want to
open during the putt stroke.
With a face-balanced putter, the shaft connects to the head of the putter directly behind the center of mass. When force is applied to the putter head during the downswing of the putt, it is applied directly at the center of mass of the putter head. This means that there is no tendancy for the downswing force to cause the putter's face to open.
Some people prefer older, non-face-balanced putters and are very good with this style (Phil Mickelson comes to mind). It seems to be a matter of personal taste. I find that with a non-face-balanced putter, I tend to miss off to the right. Face-balancing on my STX Sync Tour has helped me a great deal to sink more putts.