You will become known as an expert on the topics you write about. This will give you and your business extra credibility which will help you compete against your competition.
Your article might also be placed on the publisher's home page. If they publish each issue on their home page this will give you some extra exposure.
You might get extra exposure if the e-zine publisher archives their e-zine on their site. People might want to read the back issues before they make the decision to subscribe.
You will get free advertising. This will allow you to spend your profits on other forms of advertising. You could buy advertisements in other e-zines that don't publish your articles.
You might get extra income from people wanting to hire you to write other articles, books, or even ask to speak at seminars. This is a great way to multiply your income.
You could allow e-zine publishers to publish your articles in their free e-books. Since people give them away, your advertising could multiply all over the internet.
You will get your article published all over the web when you submit it to an e-zine publisher that has a free content directory on their web site. They'll allow their visitors to republish your article.
You'll gain people's trust. If they read your article and like it, they won't be as hesitant to buy your product or service. You will then be able to increase your profits.
You could get your article guaranteed to run in an e-zine. You could agree to run one of their articles in your e-zine if, in exchange, they run yours in their e-zine. It's a win/win situation.