Ever ride behind a semi or mini van while on a motorcycle? If so, you've very likely experienced the buffeting and steering oscillations that happen when in the right zone (or wrong zone actually). Now imagine the semi as a dull blade plowing its way through the grass rather than cleanly slicing it's way through. This being more about balance, we can overlook that for now. IF the semi driver were to move his truck left and right in his lane, that would really amplify the buffeting or cause you to be all over the place as you cruise along behind being whipped around by the buffeting.
In opposition, imaginge a GT40 cutting the air, as related to a sharpened blade slicing cleanly and smoothly through the grass. You don't usually get buffeting riding behind a low sleek automobile. the air streams that went around the vehicle join back together smoothly and quickly after they pass around the vehicle.
When there is any off plane or sideways movement as encountered in buffeting, it affects your forward speed, energy consumed and more as mentioned by CQ_DX. I see the balanced and properly sharpened blade as a straightlined aerodynamic sports car and the imbalanced blade as the erratically driven flat nosed semi.
As for the blades grind, I think it is true that a hollow grind (wheel) will throw grass better than a chisel grind (file or disc type grinder), this being a seperate issue from the lift that the sail causes.
I'm with grassman, and it's my opinion that a balanced and properly sharpened blade will give less buffeting under the deck and thus a cleaner deck as a result of more efficient discharge. It may have to do with all grass clippings being better lined up as the leave the tip of the blade. It would be interesting to see a stop action or slo mo film of what goes on under a deck during these various conditions.