Well your employer cares not a whit what it costs you to live. In aggregate though it is useful as a baseline estimate of how they are going to adjust salaries

Well your employer cares not a whit what it costs you to live. In aggregate though it is useful as a baseline estimate of how they are going to adjust salaries between locations. Remember, it’s not just software engineers. Receptionists, drivers and food service workers likely make different wages in different locales, and are not typically involved in intense individual HR negotiations.