Combined with other information, it may identify someone reliably, just like you can with zip code, age and gender. For example, if you know this person is part of a group with members in several locations, or if you can corroborate someone's movements, etc.

For example, imagine someone suspected of sharing sensitive information with a journalist. They might have a short list of suspects, and use this technique to confirm which one it is. They might identify which journalist it is - maybe only a limited number cover this beat.