I grew up with both, and don't really care which I use, as long as the lathe, mill or whatever is graduated in the same system.
A standard metric micrometer is graduated in hundredths of a millimetre, which is a smaller dimension than the thousandths of an inch a standard Imperial mic is showing. No big deal either way, and there isn't a lot outside of toolmaking that requires more accuracy than +-0.01mm (slightly smaller than half a thou).
Fabricating in mm I find easier than converting to Imperial - adding 64ths, eighths and the rest is just a pain in the butt. 620mm + 510mm is a simple thing, 2' 13/32" + 1' 6 5/64" - who needs that bs?
As for volume and weight, easy win to metric. A litre of water weighs a kilogram, a thousand of them weigh a ton and they fill a cubic metre. Thermal calcs are the same win to metric.
It's a bit like learning another language - it all seems clumsy until it falls into place, then it's easy.
Typically you would measure parts that long with a scale or a steel tape and either method is easy. And why would you be adding such dimensions anyway? Typically overall lengths are on the print. Adding fractions is too hard for you? Usually dimensions listed in fractions have large tolerances. The point is either way of measuring is pretty easy with the win going to SAE. By the way a thousand Kilos does not weigh a ton. That said are teaspoons, tablespoons and fractions of cups all that hard to follow? Quarts and gallon beyond your ability to grasp? Public school?
