https://techcrunch.com/2017/09/13/iphone-xs-face-id-raises-security-and-privacy-questions/

The new top-of-the-range iPhone does away with the home button and its built-in fingerprint reader in favor of a new biometric — called Face ID — which uses a 3D scan of the user’s face for authenticating and unlocking their device. It also replaces Touch ID for Apple Pay too.

Apple suggests this is an advancement over a fingerprint reader because it’s an easier and more natural action for the user to perform — you just look at the phone and it unlocks; no need to worry if you have wet fingers and so on. Apple is working the convenience angle hard.