If you don't do server side rendering, you don't (almost) automatically get a set of nice REST endpoints that return JSON/XML/ETC? I get that the abstraction might be nice for security, but at least for corporate intranet applications, a nicely structured, secured (e.g ODATA) webapi you query for client side rendering has the added benefit that it can be invoked programmatically with REST by other authorized parties.…
More seriously, though, it's nice to be able to just build without thinking too hard about if you're getting your abstractions perfect. To me, this is the main advantage of SSR - moving fast doesn't leave behind a wake of idiosyncratic APIs that need to be (carefully, dangerously) cleaned up later.