That's interesting. The current top comment implies that spam filters weigh DMARC so heavily that it's essential to reliable email.
Certainly if you have a DMARC policy of p=reject and then you screw up your outbound, then your DMARC policy becomes relevant, but not in a good way. I don't see the harm in not having one.
Email providers such as outlook and gmail think otherwise. Your emails will not be reliably delivered to them because you are missing a restrictive DMARC policy. Emails send without a DMARC policy are less trusted by default and more likely tagged as spam.