PostgreSQL JSONB: when does it make sense over a separate NoSQL store?

we currently run both PostgreSQL for structured data and MongoDB for documents/semi-structured data. it's working, but it's two separate databases to manage and operate. i've been looking into consolidating some of our MongoDB workloads into PostgreSQL using its JSONB column type. the idea is to reduce operational overhead if possible. for those who've used JSONB extensively, when does it truly make sense to use it over a dedicated NoSQL store? i'm particularly interested in query performance for complex JSON documents, storage efficiency compared to MongoDB, and any migration experiences you've had from MongoDB to PostgreSQL JSONB. our document structures aren't extremely deep, but they're not trivial either, and we do perform some indexing and querying on fields within the JSON.