The faster your web pages load, the better the user activity. Lower costs (for bandwidth) and higher revenues are also associated with faster-loading web pages. Google’s goal is to get every page to load as quickly as the average person turns a page in a magazine.
People dislike flash-based “Enter” pages that come up to escort you into the real meat of a site, and they don’t like pages that are slow to load. This is often a make-or-break proposition for web users, with faster sites getting more attention than slower sites.
Google’s Site Performance tools will tell you how quickly pages load based on actual data from actual users. The results are filtered so that “outliers” like the person in rural China using a dial-up connection’s page load time doesn’t unnecessarily weight the real average load time for the “typical” user of your website.
Keep in mind that the performance stats aren’t calculated unless there is sufficient data to get meaningful numbers. So if your site experiences very low traffic, you may not get site speed data reported.
Keep in mind that the speed data may also include pages that are not crawled. That means if non-crawled pages make up a substantial part of your visitors’ experiences, the performance data may not be accurate.