Google has been talking about site speed for ages. They have been working hard to encourage webmasters to make their sites faster.
To better understand where we started and what is going on today, I have created a helpful timeline summarizing what Googlers have been saying about site speed:
Official: Ranking Signal
In April 2010 Google announces they have started using site speed as one of the ranking signals. At that time, fewer than 1% of search queries were affected by the site speed signal and the signal for site speed only applied for visitors searching in English on Google.com
Matt Cutts writes a blog post urging webmasters not to panic saying that the update will only affect fewer than 1% of search queries.
Only in April of 2016 we had more clues as to exactly how Google is using the signal. According to John Mueller, page speed negatively impacts sites that are slower, rather than giving boosts to sites that are faster. I the same month Gary Illyes, webmaster trends analyst at Google, says webmasters shouldn't stress over website speed too much.
If you were looking for exact numbers, November of 2016 John Mueller recommends keeping your page load time below 2-3 seconds.
Site Speed and Mobile Search Results
In February 2015 Webmasters notice a new label within mobile search results flagging some pages as slow. This is the only actual site speed experiment that vividly affected search results page. It also didn't seem to take off.
In October Google announces a new open source initiative called Accelerated Mobile Pages aiming to dramatically improve the performance of the mobile web.
In December 2016 we had two a bit confusing notes from John Mueller: pages that load really slowly may be considered NOT mobile friendly. However Google probably won't be looking at the page speed of your mobile site as a factor.
The latter argument has been later confirmed by Gary Illyes in June: the speed of your mobile pages currently doesn't impact your mobile rankings, but soon it may.
Finally, as @PakWired reports, Google has just started certifying developers to ensure they are aware of site speed basics.
Crawl Rate and Site Speed
In January 2017: Google says site speed helps increase the crawl rate.
For Googlebot a speedy site is a sign of healthy servers, so it can get more content over the same number of connections. On the flip side, a significant number of 5xx errors or connection timeouts signal the opposite, and crawling slows down
While crawl rate is claimed not to be a ranking factor, it's obvious from the article that a faster site sends lots of positive signals to Google.
Conclusion and tips
Google has had a long way with their efforts to make the web (first desktop and then also mobile) faster. They have been working on tips, tools and triggers encouraging webmasters to increase their site speed.
From what it sound like:
- Site speed is only a negative ranking factor which can affect only really slow web pages making them rank lower
- Site speed isn't currently effecting mobile search results directly but it soon may. However if your page is too slow, it may be considered mobile unfriendly, which will effect your mobile rankings because Google only includes mobile-friendly pages in mobile SERPs, so there's a certain indirect impact
Whether it's a powerful ranking factor or just a way for Google to crawl your site faster, whether it effects mobile search or desktop search or both, it's clear that making your site faster is essential for better SEO and usability. Here are further resources to help you make your site faster:
- Stick to reliable hosting provider that will keep your site up and fast. Read more about Uptime here
- Netpeak Spider is a good tool to measure your page response time and find the slowest pages
- How can your hosting influence your website speed?
- Use Content Delivery Network (CDN)
- Leverage browser caching
- Optimize your site images
- Consider switching to Accelerated Mobile Pages. This article explains AMP, its pros and cons, very well.
- For WordPress users, here's a very thorough guide on making WordPress blogs faster
- If you don't like WordPress, they say, Wix is a fast and affordable option too
Have I missed anything? Please suggest a Googler's quote or a useful resource in the comments!
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* Adapted lead image: 
