Why is it helpful to calculate percentage?

It is easier to understand rates of changes as percents, sometimes, than as a fraction. Such as the stock market fell 70%

Also, you can compare percents and fractions are a little harder to compare. For example you got 91 percent right on your test and your friend took a similar test with twice as many problems and got 83% right. It is easy to compare the percents.

There are many other reasons!