I may be talking out of my ass here, but the key decider is your ability to maintain the conceptual integrity of your data architecture. Mongo makes it easy to

I may be talking out of my ass here, but the key decider is your ability to maintain the conceptual integrity of your data architecture. Mongo makes it easy to maintain document based data architecture, Postgres does not. But maybe you don't really need a document based data architecture, you just think you do and it's mainly not document based, only a little bit. Or maybe it's just too damn hard to maintain your concepts in a SQL database. Maintaining conceptual data architecture is hard and sometimes too hard.