Ah, I think I misunderstood that comment. From a global perspective "the benefit" compared to using passwords in a password manager is indeed exactly what I said, but I guess that user was asking more about the personal benefit on an individual level.

From that perspective it just makes the UX slightly smoother and makes it impossible for the site to screw up and leak your plaintext creds. Other than that yeah there's not a big difference compared to using an autofilled, unique, randomly generated password. Which is good, because eventually sites are going to start phasing out that latter option for the exact reasons I outlined in my previous comment.