Originally Posted by elCapitan
and after a day of trying with/without brake on multiple wings, I noticed absolutely no difference.
I've had the same experience. However, Google does reveal support for ashdec87's statements, no matter how non-intuitive. The studies I found involve twin engine planes when one engine quits. The pilot wants to continue flying on one engine, which means the dead engine's prop is going to want to turn almost the same speed as the engine that's running. To do that requires a LOT of power, hence a lot of drag.
We're not doing that with our planes. Usually the only time we're power off is landing, when more drag slows the plane down, usually what we want. I suspect at the lower speeds, the difference becomes negligible.