But the aim of Signal is default secure comms. It's supposed to easily wrap everything, from the absolutely banal to the fairly sensitive, in strong encryption

But the aim of Signal is default secure comms. It's supposed to easily wrap everything, from the absolutely banal to the fairly sensitive, in strong encryption in order to cut into the returns on performing mass surveillance. The question just comes down to who generally wants their communication contents persistent until actively destroyed, as opposed to quasi-randomly wiped out by technical snafus. If you want transient there are the time-limited messages, for instance...