Link building is essential to any website that wants to climb the search engine rankings and stay there. What a lot of people fail to understand is that this is not as simple as finding as many links as you can, no matter where from, and then adding them all in one go. If a website is to be consistently successful in the search engines, it has to possess a natural link profile.
Newsletters can make an accidental or first time visitor, who has come to your site because they saw something of interest to come back again as an interested reader. So long as they keep their subscription to your newsletter, you will have a consistent reader who will return to your site.