Features that make the same browser binary have a different browser fingerprint with a fresh user profile.

For example, faking location data, fonts, browser version, user agent, ssl certificates, available browser features, etc. Different anti-detect browsers offer different sets of features, but none will allow you to, say, pretend to be a Firefox user on Linux when you are a Chromium user on Windows, because it is possible to detect the engine and underlying system based on JavaScript and CSS behavior, if the website really wants to know that.

AFAIK, the most common use case for anti-detect browsers is competitive research, bypassing restrictions (not just location-based), and emulating specific user profile.