American here who actually likes SI units, since I do engineering stuff, so not having that debate – I know our units are dumb.
But, in common use, if you're talking about something like a bolt, or maybe doing carpentry, at what size do you go from "This thing is x mm long" to "This thing is x cm long"?
Does ANYBODY use any of the metric prefixes other than milli, centi, and kilo? I've never seen anything in real life described as "4 decimeters", and I can't even remember what the 10x or 100x prefixes are.
Similar with litres – we use mL and milligrams for medicine dosages, but I've never heard anybody use the term centilitres. Now that I'm thinking of it, kilolitres sounds "odd" as well, and I've never heard it used. What unit do you use to describe very large volumes, like an oil tanker?