There are a few main benefits.
- For hardware-backed keys they can’t be stolen aside from physically stealing the hardware. So unless your machine has malware there is no way for an attacker to authenticate using them.
- Even for software keys the site you authenticate to doesn’t learn enough to impersonate you. For example if for some reason your bank leaked some logs with PW + MFA someone could use that to log in as you (although admittedly short timeouts on MFA validity makes that window very small).
- The browser ensures that you only authenticate to the correct domain. So it prevents phishing. (Although a password manager that only fills into the correct domain also accomplishes this.)
So I think if you are using unique passwords with an automated password manager the effective benefit is quite small. However for the “average computer user” who likely has less than 5 passwords that they use for everything it forces a pretty high base level of security.




Oof, that is really not a good look. This should have been clearly disclosed and probably with a per-notification for the patch release.