Quick. Take out your smartphone. Open your website. What do you see?
If your website seamlessly reconfigured itself to be easily readable on your phone, you're in good shape. This automatic sizing is called responsive, and it's what website visitors demand today. If, however, your reading panels are too wide, if you have to move your phone into landscape mode to read the text, if your pictures run off the sides, if you have to squint . . . you have pretty much demoted your own site to the nether regions of Google search.
Why? Because 98.3% of smartphone owners use their devices to access the internet. So Google - which has a vested interest in delivering good search results - is taking its belt to sites that haven't upgraded to responsive design. If your site won't automatically reconfigure itself to any device of any size, you need to fix it now.
Consider this more of a PSA than a blog post. Let's get on this folks.