If you think about the last time
you used cubit
s to measure
something - viz., the last time you used your own body
as a yardstick
For me, it was about fitting furniture in a doorway.
The most crucial time happened in a rental lot, where
I had to measure a van by counting the number of times
I could stand next to it with my arms outstretched
plus one time with one arm akimbo: I had to see if
some sculptures would fit inside.
In both cases it worked well enough, but if it had
come down to a matter of inches I would have been
sure to bring a tape measure.
Technically speaking, what you're talking about is
rounding. Cubits are good for "close enough"
measures; they didn't count fractional cubits.