What Google is suggesting, is that it may not be necessary to download some of these files before rendering your content to your users. If you could defer some of this download until after the user starts viewing your page then you could give your users an enhanced user experience and create the distinct impression that your page is downloading faster. It's important, I think, to note that in doing so your total page load time may not be less, because these files will still be donwloaded, but your users will begin to view your web site's content quicker.
Optimize CSS Delivery
Again, this only works with CSS that is combined by the plugin. Excluded files will remain in the head. Google fonts files are excluded by default by the plugin because they load font types based on the browser that accesses the file. If these files are combined and cached, the fonts will show incorrectly in some browsers.