This is a very underrated point. It also means that an adversary can't go in long after the fact and dig up a message history from a server god knows where. A

This is a very underrated point. It also means that an adversary can't go in long after the fact and dig up a message history from a server god knows where. A lot of the eavesdropping scenarios concocted around key change in particular are fanciful. Practically speaking, end-to-end encrypted chat is often replacing email, not trying to protect secret agents hiding from the Reptilian Council.