How we built the new gocardless.com
gocardless.com
gocardless.com
In summary, I have no idea why you would use React to build a static site, but I sure hope they had fun doing it.
We basically wanted to manage internationalised static content effectively. That meant reusing markup, but also making sure that you're linking to pages in the correct locale and not trying to link to pages that aren't available in your locale.
React is obviously good for templating and its been quite straightforward to implement the internationalisation logic too. Since it isn't much overhead at all to render on both the client and server, it seemed a no brainer.