The extension allows you to copy selected text on a page as Markdown with support for features including the following

Ability to copy links, images, and selected text as Markdown.
Linked images, will have options to individually select link or images.
Formatted text such as italic, bold, strike-through, and inline code.
Unordered and ordered lists, with task lists support.
Tables, with respect to GFM.
Fenced code blocks, with language detection using info strings.

Given how much I use markdown everyday, I just can't live without it.