I disagree with you. If you need five digits of precision, 12345 mm is precise and perfectly usable (and slightly less complex than 12,345 meters). Others might just say that the machine (or whatever) is twelve meters long. And all the math you need is removing three digits.
In countries that aren't America, we use centimetres and metres. But it was suggested that yanks are a bit thick and might be happier using woodworkers units of millimetres and metres.
I'm curious to see how the arguments for using mm instead of dm varies from the argument for using imperial vs metric. You're right that there's way better units to use here, but I think mm is used out of convention. Which is the exact same reason that feet and miles are used, because everyone is used to it.