Newsletters are amazing marketing tools. They help you keep in touch with your customers on an ongoing basis.
Developing a newslatter program which will allow your business to keep in touch with it's audience would be one of the most important asset of your business.
If a customer comes to your website and doesn't susbcribe to your newsletter, then there is a very high degree of probability that he is gone forever. Retention of customers is highly critical especially in an online businesses.
Companies invest a lot in their blogs and content to attract new users through organic medium. But blog itself is a passive tool. To truly convert your traffic into loyal customers you need some sort of engagement mechanism going on. And newsletters are absolutely fantastic for it. All blogs have a small boring form widget asking for user's email id. Users in most cases totally ignore them.
But using novel, conversational experiences you can drastically increase your conversions.