The problem comes if the sender has a DMARC reject policy, and he or she sends e-mail to a mailing list which then reflects the mail to a recipient which honors

The problem comes if the sender has a DMARC reject policy, and he or she sends e-mail to a mailing list which then reflects the mail to a recipient which honors DMARC, the recipient will bounce the e-mail message, and never see it. In some cases this will cause the recipient to be automatically unsubscribed from the mailing list. If you're not using DMARC, and you're not running a mailing list, then yes, it won't affect you. But it's no urban legend.