This feature can be used to enhance Face ID performance by signing the same Face twice to provide more biometric details so that iPhone locks faster. Also, if you wear glasses, you can use two face IDs for more accuracy by using a face-to-face with glasses and another without glasses.
Apple has added the ability to recognize another face ID on the new iPhones, so users who wear glasses or sunglasses do not have trouble unlocking their iPhones.
Alternatively, you can also add a trusted face to unlock iPhone. So, instead of sharing your password with your trusted partner, you can only register his / her face as another face ID on iPhone. This will allow the trusted partner to unlock the iPhone by just looking at it. So, here's how to add a new Face ID to your iOS 1