From iMore:
“While Apple introduced iCloud Keychain year ago, the lack of any authentication check always prevented me from using it. I just never wanted to have to worry about handing my phone to a stranger in an emergency or even a friend at a conference and also handing them all my logins and credit cards.
iPhone X introduced Face ID as an authentication check, and that was great… but only for iPhone X. Now, iOS 12 adds Touch ID to the system as well, and that means iCloud Keychain is finally a first-class password manager.
If you’re already using a third-party password manager, Apple’s integrating those into the auto-fill system as well, so now it’s win/win all around.”
This wasn't mentioned in the previous article I quoted from, but this is something new I've definitely noticed and appreciate. Before, if someone had already unlocked your device, they'd have the access to your passwords because there was no added layer of security before it autofills passwords. Now, you'd have to authenticate with biometrics first (either Touch ID/Face ID) before iOS fills in the password.
And finally, you can control your flashlight via Siri!