Being a fan of Markdown and text formats in general, but living and working in a society where other formats are more often used, it's convenient to be able to convert my files to formats others can use.
And there's really only one tool for that: Pandoc.
I'm a huge fan of Markdown. There's something elegant in using textual sigils to provide contextual information. I've used it for taking notes, creating RSS feed content, producing my blog, and even in emails (I soooo wish there were a way to convert markdown within Outlook for the web and GMail!)
So it should come as no surprise that I use a variety of tools to help me when writing markdown in (n)vim.