By minimizing the HTTP request load, you can maximize the initial display speed of your content. 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, by combining the CSS files into one file and the JavaScript files into one file:
<link rel="stylesheet" type="text/css" href="/css/combined.css" />
<script src="/js/combined.js" type="text/javascript"></script>