glcoach-
Here's my overlay of d-plane on ball flight rules. I only understand a portion of what this is based on so this is no doubt a really gross generalization.
The abcde rules of brian ball flight rules I linked to above in this thread are a linear representation of the simplified rules.
What actually happens is that there are two factors, clubpath and clubface. The amount of out or in and up and down at separation forms one line in 3-D space. At the same time, the clubface direction at separation forms another line. If you connect the space between these diverging lines you get a plane with path line forming one boundary of a plane wedge and face direction forming the other edge of the plane. The plane in space looks like a piece of pizza. The ball travels 70 percent towards the clubpath boundary of the pizza slice and curves back towards face angle line. The pizza slice can vary in size and amount of tilt. Sitting on its edge would represent a straight shot.
An impact condition without a severe angled path (up and down or left and right) and with a face not terribly open or closed reduces the size of the D-Plane pizza slice and means you hit a straighter shot. If you use a lot of lean this necessitates other compensating adjustments that increases the size of the D-Plane pizza slice, so while you reduced loft and hit your 7-iron like a 5-iron, you have probably increased the size of the pizza slice and now are moving the ball more left and right. Using this analysis, a very underplane driver hit upward on an inside-out path with a low lofted face looking left and without much effective loft produces a right edge boundary out to the right, with the pizza wedge tilted down to left connecting to face line, and you get a low, snapping duck hook.
I'm sure others can elaborate and explain better than me and correct my many errors, but what you figure out is that controlling low-point without a lot of shaft lean, and without overdoing the in or out (or up or down) of path makes tighter shot dispersion possible. Mid-sole swinging pitch is easier to control than high shaft-lean front edge divot pitch.
That's my 3rd grade level understanding.