Why do we have different units for same physical quantity?

Explanation

When we measure a physical quantity, its measured value may have a wide range in order of magnitude. For example, size of a nucleus is of the order of `1 f= 10^(-15)m`, interatomic separations are of the order of `1 dot(A)= 10^(-10)m` and distance between the sun and earth is of the order of `1AU= 10^(11)m`.
So, it si convienient to have different units for the same physical quantity as it makes the expression of magnitude easier and more understandable.