The fastest way to get and render a webpage is to send one request to the server, get response and render page without any additional requests to the server. Each javascript, stylesheet, or image increase number of requests, and, correspondingly, increase render time. So, the best page structure is
<html><head>
<title>Page Title</title>
<style>[css rules required to render above-the-fold part of the page]</style>
</head><body>
[page content]
<script async src="[js file that asynchronously loads stylesheets, images, javascripts, etc.]"></script>
</body></html>
This way results in fast page rendering (and that's why it is preferable by Google), but it is quite hard to implement this technique for dynamic websites like most popular CMSs (because of above-the-fold styles varies from page to page), so it's quite usual to combine all css into single file (to have just one "render-blocking" css request only) and load javascripts asynchronously. Such an optimization is a part of MobileJoomla 2.0 that is in beta stage currently (send us an email if you like to be beta-tester), and we are going to release RC version to public in the March, 20-25, and Stable version at the beginning of April.
