Nobody in the world is aware that you have published a new web site on the web. Because, even if it is in the search engine results, it's still at the dead end of the result queue. Most of the people have already got what they were looking for from the first 2-3 pages.
But there are people in the web, who are using various feed readers like - the Google Reader, and they are always looking for crunch news, better solutions in those readers. Whenever they see there is a new web site, with interesting content, they will immediately subscribe to that site.
That's why if you publish a feed from your site, immediately you will see a few subscribers coming in. Whenever you publish a new content, your subscribers will automatically get notified, and will visit your site. The more subscribers, the more traffic you will get with every new topic you post.
Search Engine + Feed = Your complete traffic machine