The benefits of sending email directly from Salesforce are that you can automate when they go out, you can send up to 5,000 emails per day, and email templates are really simple to set up.
But any time you’re emailing groups of people, you should be mindful of the requirements of the CAN-SPAM law (which I just learned isn’t called the “Canned Spam” law). CAN-SPAM requires that emails, in certain scenarios, provide an option for the recipient to unsubscribe.
I am writing to you on my personal blog as a puzzle-solving Salesforce admin, not a Salesforce employee. Your decisions around unsubscribe options can have legal implications for your organization so please do not take anything from this post as legal guidance or means to make your communications legally compliant. That decision is between you and your lawyers.