It's really hard to understate the importance of having full control over the domain you use to promote yourself and host your content. If GitHub pages works today that's great, but if you find something better in the future you'll be able to move at will, without breaking any links.
This is not possible if you're using Medium or some other blogging platform that forces their name into the URL. They'll own that content forever, and you won't.
GitHub Pages is a fantastic hosting platform and when combined with Jekyll you can actually create a lot of rich content with git and a smidge of Ruby.
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