A recent rehash of GCN's classic vs modern bikes/kits in a wind tunnel showed Ollie, the test cyclist, pedaling slowly during the test. Presumably the lab is sticking with the current info indicating that pedaling may be less inefficient. Or at least more consistent than trying to hold the legs stationary in an aero tuck.
I was mostly interested in the theory that, beside an aero position on the bike, an aero kit -- jersey, helmet, etc. -- may be a bigger factor than the bike shape when we're actually mounted on the machine. I recently got some long sleeve aero jerseys for cool weather rides and a cheap aero helmet just to play around with. Seems to help, although I'll need several rides on the same routes over time and various conditions to be sure.
I usually pedal at least a little on descents because my legs cramp if I try to hold the most aero tuck position for more than a few seconds, especially after cresting a hard climb. Gotta keep moving my legs to clear the lactate buildup, otherwise the legs feel mushy after only 30 seconds of inactivity.
Same reason some local clubs split into different camps, mostly over disagreements about full stops at stop signs and traffic lights. Some folks prefer to keep moving so their legs don't get mushy because they're essentially sprinting from intersection to intersection. I don't trust drivers or some cyclists that much so I treat city rides as more casual and practice the traditional Idaho Stop at intersections -- including full stops and waiting for red lights at busy intersections. If I want an uninterrupted workout ride there are plenty of places outside town for that.
During a club ride this week the group split into the usual sub-groups -- those of us who don't blast through intersections gradually fall behind and reform our own group. We mostly chatter anyway. On a fun fast half-mile 4% downhill I noticed the other fellows were coasting so I didn't blast down that hill pedaling like I usually do. I figured I could hold an aero tuck for the minute it took to descend. And I was wearing a new aero jersey (not quite custom fitted, a little flappy around my toothpick forearms). So I just coasted by the other folks. Actually shaved 5 seconds off my usual pedaling approach. Although variables due to wind (light tailwind, maybe 5 mph), wet road from light rain, etc., may have been factors. The tailwind on that downhill is pretty consistent, though, so I'll give more credit to the aero kit and tuck, and maybe a bit to the damp road and low barometric pressure.