The main problem is our standardising on the mm as the base. It gives such large figures that are difficult to visualise and imply an accuracy that isn't attainable in all circumstances. As others have said, working using imperial gives the level of accuracy with the measurement. I was taught never to quote more places of decimal than is necessary for the accuracy required. When I see figures in mm, I assume we need to work to the nearest 0.5mm - in wood???
In metric, we now have the "metric foot" of 300mm which means you get short changed - and leads to errors in conversion...
We should have done what is used in France, and probably other metric countries - use metres and decimals thereof for large measurements, cm and decimals for medium accuracy and only mm and decimals for high accuracy (ignoring the scientists). They choose the appropriate base measurement rather than having everything in mm. When I buy a ruler in France, the printing is appropriate for the length. (and I bought wood in metre lengths) You also still come across people using "pouce", which is about an inch...