Especially for GitHub, I don't want to iteratively push commit after commit to README.md just to get the correct syntax for their GitHub-Flavored-Markdown. When editing on GitHub directly, I appreciate the preview to spot mistakes.

However, there are many downsides of using the website for editing (like you can't combine changes to multiple files in a single commit). I prefer using a real editor locally, but using any other Markdown processor might give slightly different results. Therefore I use flavor [1] to filter the Markdown document through the GitHub API for reviewing it locally before pushing.

[1] http://brettterpstra.com/2012/09/16/easy-command-line-github...