I heard that once it closes the valves the air that is compressed acts like a spring essentially and helps reduce power loss from the dead cylinders. Because the horsepower gets cut way way down when it goes into MDS mode it also adds throttle, but since it is drive by wire you never know that is happening.

I had an 08 Ram with a 5.7 and you could hear the MDS if you listened for it, the exhaust note(mine was all stock) would change a little bit and you could catch the added throttle weird sometimes and feel it. Take in mind I was looking for all these signs, to someone who didn't know or care how it worked you would never know.