> I can’t see any valid reason not to use Postgres at the back end

I'm using sqlite in production for a backend service. There are plenty of downsides, but to focus on the positives:

- I can run all tests in a database in memory. It's incredibly fast to "spin up" and I can use a separate database per test

- Related, I find that I write more tests against the database instead of mocking a database, which cuts down on time writing tests.

- I don't need to start a database to run the backend

- I can have snapshots of the databases in a single files for various scenarios

All in all, the development process feels a lot faster. When something takes a millisecond instead of seconds, you do things differently.