My coach has been doing the same thing for more than 15 years. He says the idea came from how skiiers adjust the bindings to ensure the ski is flat on the snow.
He's got a bunch of different thickness plastic strips (at about 1/20 the price of Lemond's wedges) that he inserts in between watching you pedal on a windtrainer. The difference (if you need this adjustment) is amazing.
I was putting a lot of pressure on the outside of my feet before adjustment and now the force is perfectly spread across the ball of the foot.