Since website is ranked according to its performance, Google used a sites' speed as part of the ranking algorithm they used. Sites that load faster ranks high than those that loads slower.
Matt Cutt of Google said, "We are starting to think more and more about should speed be a factor in Google's rankings."
Google has given a fair list why they are considering speed as a major factor for ranking websites. A fast web, according to them, will be better for users, site owners and to Google.
More productivity is what matters a lot. A fast loading website if given a boost in ranking will improve the user experience for those coming from Google. If you click a site that is on top and it takes a lot of time to load then you will definitely lose your interest to wait for it to open.
If site owners would improve their speed to appease Google, it would be better for the users as well.
Google ads are everywhere on the web. So, if site owners are given an incentive to address speed issues it will increase page views, clicks and revenue for both Google and the publishers which means more revenues for everyone.