First, let us understand what filing ITR means. When you file your Income Tax Return, it is a proof that you have an income for which you have paid tax. According to the Income Tax Act, 1961, you have to file ITR every year. Filing it provides legality to what you are earning. Not filing it means that you as a person have not disclosed your income. The ITR gives a standard proof of income to a person and helps to establish a record with the tax department.
Also, if you have paid tax more than what is required, you will have to file the return to get a refund for the excess amount paid.