They won't teach you this in Drivers Ed

Yes, that's how I learned it in driving school as well. You can decelerate using the brake only, but once your speed drops below ~25 kmh / ~15 mph you should use the clutch simultaneously to not kill the engine. And it's not harmful to use the clutch already on higher speeds since all it does is disconnect the gears - though leaving it engaged while you are not using gas means that the load on the gearbox helps to decelerate a bit faster.

[This comment has been deleted by an automated system]