Tech Support One reason to use DKIM/DMARC (and other MTA related security features)

[Tracy]

Because there are bad actors out there that will try to send emails as if they are from your domain.

This is using CloudFlares DMARC management feature. If you notice, SPF, DMARC and DKIM all failed on the send attempt and it was reported by Yahoo.
I don't see this regularly, but they do happen and it shows how quickly your domain could get marked as a spammer if you don't protect your email origination point.