[deckard1]

Code reuse. If I need to render on the server (for SEO purposes, as most people do not rely on Google's dubious and unknown JavaScript processing ability) then it makes sense to want to share as much code as possible between the server and the client. If you're doing a single-page-application (SPA) you can also share routing code, as your client will need a way to route to pages client-side.

With that said, I've seen people argue against node APIs and this desire to only use web APIs on the server. I don't get that. Node's API is generally pretty good and using JS as a replacement for Python/Ruby/etc. locally is rather excellent today. You don't need neutered APIs to also write code that works in both client and server. Unless you're selling cloud native bullshit (ahem, Nextjs)