I spent from 2005 to 2020 doing almost nothing but vulnerability research, where the modal client project was a SAAS-type app, and my experience is that only a tiny fraction of companies building on Postgres actually use Postgres authorization features. It's far more typical to build this logic into the application than to build off the database's authorization features.

Nevertheless, if you're building an app that takes advantage of database auth features, that's a powerful reason to keep on using Postgres. You actually have one of the major problems Postgres solves for!