[StudentStuff]

An alternative method of protecting oneself is to set an expiry timer, which makes messages in a conversation ephemeral. 1 week seems to be a fine balance between being able to look back at old messages, while also not having those you communicate with be allowed to store data on your device for too long.

[inferiorhuman]

Signal won't prune the messages until you open the app (or maybe the conversation) again. There've been a few releases where the changelog notes that the app didn't expire ephemeral messages properly.

[this_user]

Signal also has an option to truncate your message history automatically, i.e. it only keeps the n newest messages and deletes older ones.

[craftyguy]

That's a good idea. Even if you enable FDE and a strong passphrase, the court can still compel you to unlock it. They cannot compel you to automagically undelete expired messages (hopefully those are expired and removed in a secure mannner...)