What's ironic here is that in the adversarial setting the application is designed for, unexpected retention of user data (on end-user devices) is a sin.
I like to think about messages being ephemeral. If a piece of information needs to be saved, I just store it outside the messaging app. This includes media files, too.
That’s fine. But Signal should then advertise itself as unsuitable for general-purpose communication, primarily relevant when someone is specifically worried about adversaries reading the communication.
I can see how this makes sense for journalists, dissidents, diplomats, criminals, corporate executives, etc., but if data is under threat of disappearance, regular people should be warned away and told to use something else for day-to-day communication.
I like Signal and it always makes me happy to see more people showing up there, but for now certain group chats will stay on other messaging services.