The amount of indexed web pages is one of the main site`s features. It reflects the domain weight. Webmasters have to strive for making the number of indexed pages close to the actual number of pages.
If the amount of indexed web pages exceeds the actual one, this can be a result of duplicate content. In some cases, search engines consider duplicate content as cheating and manipulation.
Web masters have to control the presence of duplicate content on their site. It is recommended to carefully syndicate the content to other sites, use 301-redirect where needed and ban such article`s indexation in the robots.txt file.
If the amount of indexed web-pages is smaller than the actual one, the site receives fewer visits by low-frequency and mid-frequency inquiries. External links to the pages that are absent in a search engine`s index, as well as the creation of sitemaps, will help in this case.