10 microns = .01 mm = .0004 inch
Make the tolerances too tight and the body parts will interact with each other in unfortunate ways - shell gets too hot, metal expands, and you can’t open or close the doors. Window glass will crack etc.
Watch these fucking life-size HotWheels fly apart when it gets too cold or too hot.
It’s funny how Tesla’s already have a reputation for being designed with only California weather in mind, and now he plans on making them even more susceptible to such foreign concepts as “cold” and “heat”.