Curtis, there's a school of thought still out there that you will compress the ball more with more downward strike through more shaft lean (the comment in the article you linked to says this) and that you should be working to add more lean all the time. Here's a comment from Brian on this idea:
"3. Lots of folks thought, and some still think, that if you really "bang down on the ball" you will compress it more. This makes the ball go much farther.
What happens in this scenario is simply the golfer de-lofts the face, turning say, a 7-iron into a 5 or even a 4, by hitting down with a forward leaning shaft and delivering up to 10 degrees of downward and de-loft. Turns out that, given the same club head speed, the ball would go the same distance if the 5-iron was just properly struck with about 3 or 4 degrees of downward and de-lofting."
So, if, as the others above have noted adding extra lean forces more swinging left to compensate, and if, as brian says above, doing this doesn't make you hit the ball further, then why strive to have extra lean if it just forces more compensations and doesn't increase distance?