Mobile-Friendly - Algorithm Update
I don't know how many people are aware... but on April 21st, Google came out with an algorithm update which factors in your website's mobile responsiveness when determining mobile rankings at a page level..
Meaning, if your site isn't mobile-friendly, you're going to notice a drop in traffic as you'll be dumped down the mobile SERPs. Depending on your niche, this can either make a huge impact, or one that you will barely even notice. Again, depending on your niche, the vast majority of your traffic could come from mobile sources (up to 60%!! or more!).
Here's some more random facts: Did you know that this year (2015) mobile searches are on a course to surpass desktop searches? Did you know that 71% of people expect a mobile site to load as fast as a desktop site? Or that 60% of them want it to load in under 3 seconds? How about the fact that 57% of people wouldn't recommend a site based on a low-quality mobile experience?
here's a super-basic infographic with some of the same stats (please don't steal it - make your own)
These are some very good reasons to make sure your site is properly optimized, from utilizing caching to properly compressing images :)
You can use Pingdom or Google Pagespeed Insights to get an overview of your site's load-time.. Pingdom will show you the exact elements which are slowing down your site, and pagespeed insights will basically tell you to compress your site and give you a ranking /100 for both mobile and desktop, 90+ is ideal. 95 is basically perfect and it's really hard to get any better than that.
Lastly, Google has put out a tool very similar to pagespeed insights (which is linked below) that will tell you right away if your site is mobile-friendly (in the eyes of Google). It's still strongly suggested to check your loadtime on pingdom & pagespeed insights though. I don't think the pagespeed variable is factored into Google's mobile friendly test too much... So even if the mobile-friendly test passes your site, it might still be bogged down by poorly optimized images or various other reasons; which will still turn visitors away.
Pingdom Speed Test: tools.pingdom.com/fpt/
Google's Pagespeed Insights: https://developers.google.com/speed/pagespeed/insi...
Google's Mobile-Friendly Test: https://www.google.com/webmasters/tools/mobile-fri...
Google's Mobile-Friendly FAQ: http://googlewebmastercentral.blogspot.ca/2015/04/faqs-april-21st-mobile-friendly.html