I’d like to add to the reasons for why you want an SPA over something with SSR:

* You have a large number of users compared to your resources and you can’t afford for your user base to always hit your server. Comparatively, deploying API-only apps is far cheaper when you’re resource-starved (eg early stage startup).

* You don’t care about SEO, for example you’re building internal tooling. You then don’t need to care about hydration at all. Much simpler to separate concerns (again esp at the beginning).

* Offline mode (eg PWA or reusable code in Electron) or cases where you want to be resilient to network failures. In the case that your app is dependent on the server for basic functionality like navigation, you can’t support any type of offline mode.