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.
Using millimeters is pretty common in engineering.
I’ve seen technical drawings where the dimension of something is 10000+ mm. At that point I feel like the whole utility of the metric system is moot.
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.