Using engine brakes can cause your car to not use fuel in some cases.
I've read and heard this from different sources (even driving instructors) and I don't get how it's possible. Your engine is still running, doesn't it use at least as much as it does while it's idling?
Edit: thank you all for your answers. I knew how the engine brake effect worked, my confusion was about exactly why the engine didn't consume fuel in the process. I now understand so thanks all.