Search engines are like school teachers they do not want your web site to fail their test for relevant information, they just want the best to get on the top of their index so their customers who come to them looking for information can be presented with only those sites that have the most relevant information.
They are also like researchers, constantly looking for new sources of the same information without compromising on the quality of the information.
So, it will always prove beneficial to keep changing the content of your site to suit the search engines.
It may not be possible to constantly keep upgrading your site with fresh content every month or even two, but it helps to constantly write fresh articles and post them to article directories for better exposure.
It is a fact that articles posted on the various directories get top rankings and thus make the site rank higher in the search engine indexes too.
The way I look at it is that the article directories are such a rich source of information with so many hundreds of thousands of people writing and posting on various topics daily that the article site becomes a rich source of keywords and key phrases that the search bots are looking for.
Add to this the huge traffic the article directories get each and every day then compounding this ranking is the fact that people can pick up and post articles on various sites as long as they post the URL of the article too.
This leads to massive back linking of the article directory which, in turn, allows the article directory to get the highest ranking on the search engines.
Now when an article marketer writes optimized articles and posts to the article directory the article rides on the ranking of the directory thus presenting the keyword rich article to any searcher on the net.
The article directory allows the writer to post a back link to the site he or she is promoting in what they call a 'resource box'.
This resource box is the only place one can place a URL of a site, which is invariably the URL of the site the author wants to promote.
This again leads to back linking of the author's site and increases ranking of the site being promoted.
So, when it comes to promoting your site using the services and established indexing and ranking of the article directories, article marketing is the best practice - make the most of it as most directories offer free article posting services.