Author here.

I really think there's a lot of value in this model for users to self-host apps. PostgreSQL can run cron jobs, operate on external data with foreign data wrappers, and even do some number-crunching with Madlib right within SQL.

So, the user only has to manage a postgresql db, retains control on data and can easily get upgrades of webapps via CDN and mobile apps via app stores. Developers benefit because (a) there is no server-side programming language to deploy/maintain and (b) PostgREST API is very well thought-out and very predictable - leading to easier development across frontend/mobile frameworks.