Let's face it: Writing content for the Web is tiresome. WYSIWYG editors help alleviate this task, but they generally result in horrible code, or worse yet, ugly web pages.
Markdown is a better way to write HTML, without all the complexities and ugliness that usually accompanies it.
Some of the key benefits are:
John Gruber, the author of Markdown, puts it like this:
The overriding design goal for Markdown’s formatting syntax is to make it as readable as possible. The idea is that a Markdown-formatted document should be publishable as-is, as plain text, without looking like it’s been marked up with tags or formatting instructions. While Markdown’s syntax has been influenced by several existing text-to-HTML filters, the single biggest source of inspiration for Markdown’s syntax is the format of plain text email. -- John Gruber
Grav ships with built-in support for Markdown and Markdown Extra. You must enable Markdown Extra in your system.yaml configuration file