Obviously keeping data off-chain helps if you want mutability. It's also cheaper and faster. I could imagine a social network where only identities are on-chain.
You could also have the hashes of the content on-chain, so that subscribers could determine if they are receiving only a subset of the posts on the feeds they are subscribed to.
The trade-off for this feature, of course, is that a publisher wouldn't be able to plausibly deny having ever written some archived post which later gets them in trouble, but if you're only sharing posts with your friends, and their servers respect your delete requests, this might not be a problem in practice.
just the hashes on chain would mean a central org can censor anytime .. they wont be any diff than twitter.. the biggest problem with bitclout like on chain socials would be that people wont be able to change for the good or obv go back on what they said.