I recently came across a site that had the following code: <link rel=dns-prefetch href=//ajax.googleapis.com>In looking it up it says it is used to Reduce DNS lookup time by pre-resolving at the browser.So my question is, other than (hopefully) making the site feel a touch more faster, does it have any other impacts on SEO or the site in general?
SEO and other impacts of using rel=dns-prefetch
seo;dns;rel dns prefetch
Google and other search engines ignore tags they don't recognize and directives that are not specifically geared towards search engines.  As such there will be no direct impact on rankings.  Search engines won't use dns-prefetch as a direct ranking signal.There are indirect SEO benefits when your site is faster.  Google does measure how users react to your website.  Do they hit the back button because the site is too slow?    If using  dns-prefetch makes your site appear more quickly to users, then by all means use it.  See: Why is loading speed of a website important for SEO?