Let's look at the fraction 5/75. 5/75 as a percentage is 6.67%. This tells you how much of a whole the fraction represents in everyday terms.
The fraction 5/75 can be reduced to 1/15, which is a simpler way to see the same value. Whether you write it as 5/75 or 1/15, the percentage stays the same.
Knowing the percentage is handy for quick comparisons. For example, if you see a discount of 6.67%, you now recognize that it comes from the same ratio as 5 out of 75 parts. This makes it easier to understand small changes in numbers.