This is another of the early Policies which accelerate military units' production time. It is usually much more useful than Maritime Industries (since making cavalry is always useful); however, note that you will only have real use for it if you truly intend (and need) to build cavalry units (this means the Horseman); and if you have Horses. Otherwise the only unit that benefits from it is the Heavy Chariot, and its File:Civ6Production.png Production cost isn't that great anyway. In such case you'll be better off using your Military Policy slot for something else.