It is to see if you qualify for earned income credit and if so, how much. EIC is based on the number of children you claim as dependents, your filing status, and how much income you earned by working.
The IRS also offers a tool to help you estimate your EIC:
https://www.irs.gov/credits-deductions/individuals/earned-income-tax-credit/use-the-eitc-assistant
https://www.irs.gov/credits-deductions/individuals/earned-income-tax-credit