So what is a good use case for Mongodb? I have never seen an application where a "document database" would have been a good choice. In every project where I have seen Mongodb, it has turned out to be the wrong choice.
Even for prototyping there are many other good choices since RDBMS like Postgres have implemented JSON support. Mongodb looks like a solution in search of a problem.
Is there a benefit of Mongo for that over just Postgres with JSONB columns? You're still storing JSON in Postgres but you'd get the relational aspects too for things like users having many forms, billing and account relationships etc.
No benefits that I can think of at the database layer. Postgres's addition of JSONB columns represents the best of both worlds. Funny to think that all of that noise about nosql replacing rdbms was essentially nullified by the addition of one column type.
Easier horizontal scaling and organizational inertia would be the main reasons to use mongo over a jsonb column. I wouldn’t introduce it to a psql shop if they are already great at running psql.
Even for prototyping there are many other good choices since RDBMS like Postgres have implemented JSON support. Mongodb looks like a solution in search of a problem.