[paxys]

Look up server-side rendering in React. The major benefits are better/faster first page load experience and better SEO, especially for crawlers that don't have good JavaScript support. This way you can run the same code on the client or server depending on the circumstances.

[nobleach]

The fringe benefit being I don't have to represent my app twice (once for server-side markup, the second for client-side JSX). As the size of any give app grows, keeping things in sync would be a nightmare.