Why do we do accounting?

I am not in this field, however I see it very interesting to tackle this question.

The main purpose of accounting is to keep track of all the financial transactions made by a business. Thus, the primary purpose of accounting is to check the performance of a business (revenue vs. expenses), i.e. is the business is successful or falling. 

Another benefit is accounting can help to increase the revenue of the business and limit the expenses.

There are many other benefits for accounting, however I only highlighted some major points.