Units of measurement provide a standard to measure mass, length etc.So, it is useful.
because it is.
Units of measurement are useful to rationally measure anything.
To estimate numbers more easily.
NO
penis
significant figure
Rounding is useful in the following two situations:round allows an approximate answer to be obtained quickly rather than a precise one after a lot of time and effort;when information is provided with a spurious degree of accuracy: for example, the average mass of adults given to the nearest milligram.
Tonnage is used as a measurement of cargo ships.
au
useful
you will use cm because it is useful then the other types of measurement