I have to use both sets of wrenches and socket tools for my vintage Datsun (Nissan) cars from the 1960s and 1970s. Half the car had metric bolts, and half the car had U.S. measure bolts. Some engine components were originally derived from British designs that were licensed by the Japanese for their engines way back then and were metric. They adopted U.S. measure for body and some engine components.
Then there's the BSF and BSP.
If you've never experienced British blokes discussing threads and spanners, count yourself lucky.