Almost BenDover, try it, fly idle throttle, RPM set to full (RPM is always set to full even if you idle the throttle UNLESS you manually lower the RPM which takes a few seconds). Try and glide near the ground, see how long you stay up or how far you go.
Do the same with the engine shut down (in a plane that stop the prop from spinning).
All props work as thrust (most props are "pulling" the plane, there are some that pushes the plane aswell). BUT All props also work as a breaking force, when the speed gets too high the breaking force is bigger then the pulling force which is the reason prop planes can't go supersonic.
Like I said, try it, you will notice that you glide far longer with RPM set low or engine killed then with engine on idle and RPM high.