I thought it was a massive use case for Facebook. I recall seeing Facebook engineering tech talks about how they write their JavaScript with different types of import statements to optimize what gets rendered in SSR versus on the client. I think this is a similar video: https://www.youtube.com/watch?v=KT3XKDBZW7M
> The HTML output by this stream is exactly equal to what ReactDOMServer.renderToString would return.
I imagine this returns a stream as a convenience for Node servers that are streaming chunks of HTML. I don't think it means that React's SSR is rendering chunks of HTML in an async fashion and returning each chunk to the stream as soon as it's ready.
You're right. ReactDOMServer.renderToNodeStream is to support HTML streaming, which can allow the browser to start rendering the (as far as it knows, static HTML) document before it receives all the HTML. This is nice, but probably is not a huge factor if you're using HTTP caching via a CDN or a static site generator (since the CDN will likely support HTML streaming).