If you base your units on what is practical, then it's retarded. You'd have one unit of height for measuring human beings, another unit for measuring houses, another for measuring the sizes of cereal boxes, and so on. The whole point of units is that they're standardized. ALL THINGS must be measured in terms of how far it takes for light to travel in a vacuum during the time it takes for 9,192,631,770/299,792,458 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.
Also, it's not the metric system's fault that Europeans are retarded and don't add significant digits. I'm 1.8m tall. If Americans wanted, they could say "I'm about two yards tall," but we don't, because that would be stupid.