There are a number of reasons you may want to file a tax return even though there is no obligation to do so:
If taxes were withheld from your pay, you must file a tax return to receive a tax refund.
If you qualify, a return must be filed to receive the refundable Earned Income Tax Credit.
If you are claiming education credits, you must file to be refunded the American Opportunity Credit.
If you have a qualifying child but owe no tax, you can file to be refunded the Additional Child Tax Credit.
If you qualify, you must file to claim the refundable Health Coverage Tax Credit.
If you adopted a qualifying child, you must file to claim the Adoption Tax Credit.
If you overpaid estimated tax or applied a prior year over-payment to this year, you must file to receive the refund.