Did you ever signed up to any newsletter? People sign up to newsletters because they would like to receive some useful information in the future. If you have an online business or even a blog, then you might want to encourage your visitors to sign up fro a newsletter. The advantage of it is that people will not forget about your site as they will be reminded about it on a regular basis. Some webmasters send newsletters on a weekly basis, while others send on a monthly basis. It really depends on you as there is no magic formula. Just make sure that your newsletter are informative.