Member-only comments not only give people a reason to become a supporting subscriber, they also allow you to have a healthy dialogue. That means your comment section won’t get over-run with spam or drive-by haters, allowing you to build a community without spending hours per week moderating and dealing with abuse from anonymous trolls.
You can set up your comments so that everyone can read them, but only paid members can comment, or make it even more exclusive so that only paid members can see the comments. This makes moderation simple.
To do this, Outpost integrates Cove Chat, a Ghost-specific commenting system. It ties into Ghost so that your members don't have to set up another log-in and password, all they have to do is be logged in to your site in order to comment. Cove is cookie-less and privacy-protective.