If you have a connection pooler in your application, and the DB is only used for this application, you don't need an external pool like PgBouncer. That is probably a pretty common scenario, and typical web frameworks include a connection pool anyway.

An additional complication is that more aggressive pooling methods have side effects that you must know and prevent in your application. They're not safe to use out of the box.

The need for a connection pool is a side effect of the heavy process-based PostgreSQL connections. And I would suspect that this will change at some point in the not so near future, so that users don't have to think about this part this much.