It's about complaints, say your unsubscribe link doesn't work or if there's any other issues. Then the recipient will have no other option than to report your server, which forces a manual check, which means a huge waste of time.
This is basically why you pay extra for short term SMTP enabled servers. They know they will generate a ton of extra work due to spammers, false reports and similar.
The more compliant your emails are, the more likely any Karen receiver will contact you directly instead of authorities to stop the spam. And as rule 3 suggest, you should honor the receivers opt-out requests to avoid trouble or service interruptions.