For secrecy and access, just relying on end-user keys and encryption is not good enough for me - e2e encryption UX is tricky (key management, backup, access from multiple devices, onboarding), and tends to turn less technically minded users away (or they lock themselves out by not properly backing things up).

For history rewriting and sanitizing: I mean, someone posted something that needs to be removed before it's seen by a wider audience. I don't know, customer PII in the wrong component, abusive content (eg. dox) on a public tracker or internally by a disgruntled employee, server logs in an attachment that should be removed a year after having been posted (in accordance with a privacy policy), etc. I want to ensure that content can be nuked, and access to sensitive data revoked. This is also another reason why secrecy via e2e encryption in a fully decentralized system doesn't work for me: if a user's key gets compromised, all secret data that this user had access to is forever accessible to the attacker. With server-side access, it can be revoked, which helps if the data has not yet been downloaded. Plus you can keep an audit trail to detect any attempts at data exfiltration, while data exfiltrated by key compromise might never be detected.