Optimize Blog Comment
Most blogs allow comments, and when the commenter fills out the required information they must put in a name, email address, and the comment. In most cases they also can include the URL of a web site. If the administrator of the blog approves the comment and it becomes a visible part of the blog, that link to that website is retained in memory and becomes a link to the blog commenter’s site, something that the search engines will consider when ranking that site. The more links into a site, the higher potential ranking the site can achieve. Of course there is much more to SEO than incoming links, but just by itself, it’s a powerful tool for SEO when done properly.
Recognizing the potential power of those link spawned the rise of spam comments done both manually and automated. Blog owners can usually add spam filters to eliminate much of the problem with the automated commenting systems, but spam placed manually is much more difficult. My rule of thumb is that the comment must refer to something in the post to be considered worthy of being approved.