Got to agree, there is minimal pedal lift when the chain shortens. Granted, 50% is removed by the derailleur, but 50% goes to lifting the pedal by a couple of mm.
I am not a downhill expert so I can't really comment, but this may have some merit for keeping your feet on the pegs while sending it across some really, really rough terrain?
From a mechanical point of view, this slight lift while under power may put undue stress on the motor but I have yet to see damage from it? Although, it would be interesting to see if there was any real long term benefit to the Brose sprag bearings for example?