I will say it's still necessary and a good practice for users to do before they are in a crisis point with a hacker handling their account.
The initial idea behind signing a message was that other users verify and quotebyour message, so even if a hacker gets access to your account and deletes all traces of an address, it's still available in the quoted messages on that thread. Post scrappers from users like LoyceV and TryNinja have fixed this issue to an extent, there will always be an archive of posts made on the forum.

All users should still be encouraged to sign a message early on to insure their accounts, cause not all participate in signature campaigns.