I disagree on two points made. I am new to this too, so please tell me if I am wrong!
An idling GLOW engine will produce drag as the propeller will idle at a fixed speed. Any wind trying to accelerate the prop will fail to do so, and thus increase the resistance. With an electric motor without the break set, the propeller is free to spin up faster since there is no compression holding it back, and thus the windmilling propeller is not creating any drag. The break on an ESC will apply a resistive force to the propeller (like compression), so a stopped propeller will create more drag than a free spinning propeller. The break settings on some ESCs are variable, so you can adjust the amount of resistance to the spinning prop. A high break setting will/should stop it completely, whereas a lower break setting will let the prop spin but at a fixed rate.

Having an idle RPM is beneficial in many maneuvers, such as snaps and stall turns. The prop wash over the tail will help the plane through these maneuvers. Full scale planes have an idle RPM and use that to their advantage in many instances. Of course there are times when the idle RPM can be a negative thing, such as trying to land on a short field. The beauty of electric flight is that we have full control of this throughout the flight.

In precision aerobatics, we use the break function to slow the plane down on down lines, when gravity is trying to accelerate the plane in a vertical dive, or a similar attitude. If you want to the plane to glide, you want to turn off the break function and let the propeller spin naturally with the wind. Any force you apply in resistance to that natural spinning of the prop will work against the forward motion of the airplane.

I just started flying my electric pattern plane. I tried with the break on at first, as it was suggested in the forums related to my airplane. While it really does slow the plane down in a vertical dive, or coming down the back side of a loop, it also slows the plane down when gliding through the air. It was later suggested to me to leave an idle rpm until I got used to the feel of the plane and of electric flight, then I could start playing with no idle and playing with the break. Subsequent flights have really given me the benefit of flying the plane in a manner that I'm used to, and getting to learn the characteristics of the plane before having to learn the characteristics of electric flight.