By combining external files and embedding CSS and JavaScript within your HTML you can minimize the number of HTTP requests required to render your page. Each unique HTTP request requires a round trip to a server, introducing indeterminate delays.

So this:

<link rel="stylesheet" type="text/css" href="/css/fonts.css" />
<link rel="stylesheet" type="text/css" href="/css/nav.css" />
<script src="/js/functions.js" type="text/javascript"></script>
<script src="/js/validation.js" type="text/javascript"></script>

Becomes this:

<link rel="stylesheet" type="text/css" href="/css/combined.css" />
<script src="/js/combined.js" type="text/javascript"></script>