Of course, the other consequence of being able to delete unilaterally is that message history is no longer a "redundant backup" - one person's mistake can delet

Of course, the other consequence of being able to delete unilaterally is that message history is no longer a "redundant backup" - one person's mistake can delete everything. Furthermore, chat transcripts can change silently, which may have various consequences. Telegram deleted messages are not shown as placeholders, but just disappear. On the other hand however, unilateral delete does help the use case where people want to minimize the chance that the information is accidentally leaked or exposed - the "store less info" strategy