Most businesses exist to make a profit - if a business makes large profits then it is successful. Even successful businesses want to increase profits and become more successful.
Businesses work out the percentage increase or decrease in their profits from year to year - it makes it easy to see how well they're performing in comparison with other years.
Also takes into consideration profit or loss from one-off events and financial costs, e.g. interest payments and tax. It's the measure of profit that dividend payments are based on.
Measure the relationship between the profit made and the sales revenue. They tell you what percentage of the selling price of a product is actually profit.