A NEWSLETTER IS GOOD FOR:
Building a base of loyal customers.People who opt in for your newsletter are highly interested in listening from you.
Share quick news with your customers.
Present your customers with product news (product arrivals, exclusive opportunities). You would write a few lines and point the customer to the product page or to further info on your blog/site). Tip: including photos in your newsletter turns into high click through rates (i.e. customers clicking to learn more).
Share "exclusives" with your customers.
Those who opted in for your newsletter should be given special treatment. Reward them with special news/opportunities/service previews/product previews/discounts/invites, etc, that will (or not) be released to the rest of the public a few days later (on your blog).
Newsletter = content. Search engines love content.
It's about re-purposing your content. Your newsletter can have both an email and an online version. (note: if your newsletter features "exclusives" only targeted at subscribers, it makes sense to take it online a few days/weeks later)
Increase traffic to your site.
Once you have built a good fan base, any time your release a newsletter you'll see spikes in your site's traffic. That traffic may not be interested in what you're offering through your newsletter but may be interested in other products, may bookmark a page for future reference, or may consume (and share) content from your blog. Again, you keep them within your "environment".
Followup marketing.
Of course it depends on the market, but research proves that it takes 7 followups to convert a prospect into a customer. Basically what this means is that you may not be able to have your customer buy on the first try, he/she may have to be exposed to several newsletters before buying from you.
Regular contact.
Your newsletter is something your subscribers expect to get on a regular basis, maybe once a week/month. Regular contact strengthens the relationship between two parties.
Immediate sales.
This applies to one-of-a-kind products. You would release your newsletter to your subscribers with an "exclusive opportunity". Include complete contact details (even the name of a person customers should call/email) in order to close the sale asap.
A BLOG IS GOOD FOR:

Show you're the authority.
Become an authority in your niche by providing how-tos, product reviews, informative articles. Shoppers will look to you for answers, and will eventually buy from you.
E-commerce + information.
Search engines give more weight to informative sites with fresh/quality/useful content. Show Google your eCommerce store is not here just for the money, you also want to share your knowledge.
Please Google.
Google is now able to identify and favor "engaging" websites. The more interesting your content is, the more it'll be shared on social networks and the more time users will spend on your site.
Companies are run by humans.
Show your human side. Blog about personal/company stories, anecdotes, and other topics that show there's human beings behind your site. Putting a face to your company will help you connect with your customers and strengthen the relationship.
Make announcements.
Get the word out about events, new products, site improvements, etc.
Site structure.
Improve your site's internal link structure. Each post is an opportunity to point links at your product pages. Search engines favor sites with a good internal link structure that helps them crawl and index your site easily. Improve your sites usability with in-content links that allow users to navigate your site in a natural way.
Showcase your content.
Show other bloggers/site owners the kind of content you're able to produce. This will open the door for future guest blogging opportunities (i.e you posting your content on their blog, it's a win-win proposition: they get authoritative content while you spread the word about your site)









