The article talks about this. If you have a project that starts small and an in-process DB is fine, but you end up needing to scale up then you don't have to switch DBs.

So the usecase is: I started with SQLite, but now I have too many terrabytes to fit on one server? That seems.. very uncommon.

And since moving it out of process, and even to another network, is going to make it much much much slower. You're going to need a rewrite anyway

Thanks. Serves me right for commenting without reading the article.