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.
