In most practical applications that I've seen fractions of imperial measurements used, it tends to be in powers of 2, i.e., 3/16 inch, 1/4 mile, etc. Decimals can certainly be used, but for most applications where you'd use something like a "millionth of an inch," it's vastly more common to use metric.

Or nothing is stopping you from using things like 1.3 inches, 2.7 miles, .6 gallons. I tend to use the fractions when doing measurements in my head. But if things get too complicated and I have a calculator I switch to decimal.