The two main advantages are:
  Being able to maintain regular contact, and
  Being able to build a relationship with your subscribers
Newsletters allow you to maintain regular contact with your website visitors. This is vital to success because rarely do people buy on their first visit. In fact, people usually have to be exposed to an offer 7 to 10 times before they actually buy. A newsletter allows you to
keep the connection with your site visitors, reminding them of how your product is suited for them.
Newsletters give you the "excuse" to send potential customers emails packed with articles and, of course, your sales message. Newsletters are great for building trust and relationships online. If your newsletter provides consistent quality content your subscribers can really use, they will start to trust your opinion and begin to feel that they know you. This is important, as developing relationships is vital for every business.

The other often overlooked advantage of having a newsletter is the income it can generate, not from selling your products and services, but from selling advertising space in it. You do need a medium-to-large subscriber base before other businesses will be interested in advertising, but this is not that hard to achieve, especially if your newsletter is regularly full of quality content. You can earn a few hundred bucks extra every month just from advertising if you play your cards right.

Many of your subscribers will eventually become your customers if they trust the information you regularly send them. Put simply, a newsletter is a way to build trust with your subscribers by providing value. If you help people online, eventually they will buy from you.

However, running your own newsletter involves a considerable amount of work. It is vital that you regularly write or acquire quality content before your next newsletter mail-out. Ideally, a newsletter should be sent out every week or two. This is not always easy. In fact it's never easy; the next thing that adds to your work load when it comes to newsletters is maintaining your email addresses. Many of the email addresses may be wrong because some people subscribe with an invalid address or people change their email addresses. Maintaining a list of working email addresses is crucial.