[mslot]

True, though I'd phrase it more as a middle ground. Which model is best depends on your needs.

A big advantage of schemas over databases is that you can access different schemas over the same connection, which allows much higher density, since connections are a scarce resource in PostgreSQL. You can also have shared tables.

A big advantage over row-based sharding is that you can have variations of the table definitions or a different set of tables altogether in each schema. Plus for the purpose of sharding it's easier to use, since normalized data models complicate row-based sharding.