No they won't benefit that person and in fact opens THEM up to charges of TAX FRAUD even though they did nothing wrong.   That's assuming that there were any taxes withheld other than SS and Medicaid.   If the original person was laid off this could hold up their unemployment claim for months (or worse require them to pay back benefits received in a lump sum that they don't have).  Not to mention the easily possible ruined credit score and denials of credit based on their income but 2 people worth of credit usage.   In almost no scenario does she suffer but the person who had their identity most certainly does.    If you don't see how that would negatively impact the other person you are being willfully blind.