Eh, there are pluses and minuses to deleting messages.

For me personally, having tons of ancient, many years old, emails and other messages with Isis Lovecruft and others saved my ass when she falsely accused me of rape. And I would have been even better off if I had more.

...and yes, in court she never even tried to contest the validity of any of the non-digitally-signed messages. Claiming stuff was faked is an uphill battle. Especially against the guy who created OpenTimestamps...