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If you stick the following meta tag in the of a page, Google and Bing won't show cached versions that page on search results pages: It shouldn't have any impact on SEO.  It only means that archived versions of pages won't appear be provided by the search engines on search result pages. As far as reasons to do this, we use it on pages of our site where the cached page would be blank, because the page contents are loaded by AJAX, and the cached versions wouldn't load that content.