Imperial gets tricky real quick as soon as you need to mix additions/subtractions with multiplication/division which happens surprisingly often in building.

eg: imagine you have a 5 & 1/2 foot cabinet with 4 equal sections framed out with 3/4" boards, what is the height of each section? It's (5 & 1/2' - (5 * 3/4")) / 4 which I guarantee nobody is working out in their head easily.