We never know when those files are being blocked and causing issues for your website. On March 2015,Google has announced that Webmaster Tools will include a Blocked Resources Report to help and identify these types of issues.
It will first show you where the blocked resources are being hosted. Click on the host ,to generate a drop down list of all the blocked resources along with the pages where they’re rooted. It will also suggest you the steps you would need to do to resolve the issues.
why these files are so important? Web master tool (Fetch and Render) shows you why they matter. Submit a URL in webmaster tool ,it will show you how the page looks to a regular user as compared to Googlebot.
If you have a plenty of¬ blocked resources, then Google will recommended you to start using the ones that will create the greatest visual difference when they become unblocked. in the blocked resources report.
Google will see only those files from the hosts which are seen or used by many different sites