There is some value in consuming a mix of both push and pull content. In the modern world we've gone way overboard on only consuming what we want exactly when we want it it. News letters are more like a magazine or newspaper subscription where you're choosing to have content randomly pushed at you to broaden your horizons. Also as a content creator it enables you to write differently for a smaller but way more engaged audience. It's like the difference between having a private conversation with a large group of friends versus getting on your soap box on the street corner.