When you say net income, this means that you are getting to know the income that has been received for a certain period of time. For example, you would like to know the income that the company has generated in a span of three months.
This is something that you can expect with net income. Cash flow, on the other hand, is known to be the amount of cash that is flowing in and out of the company on a day to day basis.
How much money is going into the company, and how much cash is flowing out? It is important to monitor these things because it will be easier for companies to determine if the things that they are doing are actually important or not.