Wow! The YouTube video in the last citation at the end of that APSP study is pretty damning. With only 11" of water above the drain, to see the blue dye just float past it is pretty impressive. I think there's probably some effect on the residence time of the dye over the drain by how far you position the main drain from the skimmer but the drain definitely seems to provide very little suction.

The only good I ever see my MD possibly doing would be to act as a secondary source of water to the pump should the skimmer become clogged. However, I have yet to find a dead raccoon plugging up my skimmer basket