The Style Guide for Google’s open-source projects includes some interesting recommendations that I hadn’t seen before, including:
For file size optimization and scannability purposes, consider omitting optional tags. The HTML5 specification defines what tags can be omitted.
This includes tags like <html>, <head>, and <body> as well as closing tags for elements like </li> and </p>. The difference can be rather stark. An extremely basic page may look like:
<!DOCTYPE html>
<title>A page about nothing</title>
<h1>Introduction</h1>
<p>Also the conclusion.