Not only is it important to offer your audience a simple and easy way to view your website on their devices, Google is aware of your website's ability to serve up a modern and mobile website and they will rank you accordingly. More Google weight placed on having a mobile site experience.
It has been said that we live in a world where mobile (tablets plus smartphones) are going to be more important than the desktop browser viewing. This has already happened in online retail. We also know that Google cares deeply about the user experience – they don't want to send users to sites that offer a bad experience because it's bad for their search engine to do so.
At first, it was our assumption that websites with no mobile implementation might suffer in Google's search rankings in the beginning, at least when the user is coming from a mobile device. If mobile devices represent more and more of your audience traffic then we are suggesting now is the time to make sure your site is mobile optimized.
Helpful information from Google.com
Most mobile browsers do not render Flash-based content. Therefore, mobile visitors will not be able to use a page that relies on Flash in order to display content, animations, or navigation. We recommend designing your look and feel and page animations using modern web technologies. Read more about Look and Feel in our Web Fundamentals guide.
Viewport not configured
Because visitors to your site use a variety of devices with varying screen sizes—from large desktop monitors, to tablets and small smartphones—your pages should specify a viewport using the meta viewport tag. This tag tells browsers how to adjust the page's dimension and scaling to suit the device. Learn more in Responsive Web Design Basics.
This report shows those pages with a viewport set to a fixed width. Some web developers define the viewport to a fixed pixel size in order to adjust a non-responsive page to suit common mobile screen sizes. To fix this error, adopt a responsive design for your site's pages, and set the viewport to match the device's width and scale accordingly.
Content not sized to viewport
This report indicates pages where horizontal scrolling is necessary to see words and images on the page. This happens when pages use absolute values in CSS declarations, or use images designed to look best at a specific browser width (such as 980px). To fix this error, make sure the pages use relative width and position values for CSS elements, and make sure images can scale as well.
Small font size
This report identifies pages where the font size for the page is too small to be legible and would require mobile visitors to "pinch to zoom" in order to read. After specifying a viewport for your web pages, set your font sizes to scale properly within the viewport.
Touch elements too close
This report shows the URLs for sites where touch elements, such as buttons and navigational links, are so close to each other that a mobile user cannot easily tap a desired element with their finger without also tapping a neighboring element. To fix these errors, make sure to correctly size and space buttons and navigational links to be suitable for your mobile visitors.