Except for in the military and science and anywhere else where it actually matters.
One of my more unpopular opinions is that I actually like our mixed system. Feet and inches are much more intuitive to a near approximation than are meters and centimeters, at least at a close-range human scale.
Joke's on you, rest of the world: your 2440mm x 1220mm x 13mm sheet goods, for example, are just 4' x 8' x 1/2" in disguise. Ditto for a lot of building materials, as well as standardized parts for other industries (like the pin pitch of electronics connectors etc.) that were really U.S. standards first that everybody else then got stuck with.