[jedberg]

I think it twitter's case it was architectural. By treating tweets as immutable the could publish them on a pipeline and not worry about duplicate copies around the system being out of sync.

[mattnewton]

That and early on it used sms as one of the interfaces, which is not editable.

[jedberg]

They could always send another SMS with the edit. :)

But yes, that too. The whole system was designed around SMS which couldn't be "unsent".