How Twitch Uses PostgreSQL

First question: I found the credential rotation interesting. The scheme that you describe does seem to provide a highly reliable way to change the login account/password occasionally with nearly zero chance of human error causing the account to become invalid. But what I don't understand is WHY you want to do this. What threat profiles are you protecting against?

(Yes, I know this is HN, and I used "you" as if I were addressing the author of the article. But you know what I mean.)