Because of conventional golf wisdom, I've always had my clubface centered on the ball (i.e. at the sweetspot) at address.
Now, I have never really looked into this, or applied it to my game, until recently (yes, what a shame) -- that is 2-J-1.
So at address, the ball must be toward the toe of the clubface, otherwise you would have to shorten the radius of the stroke .
And the reason Homer gives is that at Impact, the club is above the ground since it must hit the ball first before it hits the ground (Ben Doyle: "ball-turf"). Club ain't soled at Impact. So if you have the clubface centered at Impact with the club slightly hovering, and the sole it, you will now find the ball more towards the toe.
Any other reasons?
The face is opened at Impact, as it only needs to be square at Separation. So if you center the ball on the face while it's opened, and then square it back again, the ball will be towards the toe.
Also, because the clubface/head continues down-and-out until Low Point, and the fact that the clubface must be soled some distance behind the ball (you can touch the ball at address!) at address, means that you want the ball towards the toe of the face if you want it to be on center at impact.
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