Or you can run postgres on the same machine as the application, which lets you much more easily migrate if the time comes when you need to scale to multiple application servers.
There's a world between "local file" and "network DB server", running a DB server locally has lots of benefits from being able to easily query from outside if needed to forcing you to consider concurrency without the latency overhead of a network hop.
This decision tree doesn't make much sense to me. Why you someone forego performance today in favor of adding a completely unnecessary network layer to every DB query in order to "satisfy" future imaginary "scaling concerns"?
There's a world between "local file" and "network DB server", running a DB server locally has lots of benefits from being able to easily query from outside if needed to forcing you to consider concurrency without the latency overhead of a network hop.