Question

Why is it useful to write a ratio of fractions as a unit rate

Answer 1

A "unit rate" has a denominator of 1. That will often simplify any subsequent math operations.

The choice of the form of a ratio should be made based on what you need to do with it. Sometimes, a denominator other than 1 is appropriate to follow-on operations you may need to perform.

Answer 2

The unit rate has a denominator of one.This will often modify any subsequent mathematical calculations. Choosing the form of the proportion should really be based on what you're doing with it. Often a denominator apart from 1 is sufficient to follow-up operations that you will need to run.