Absolutely agree that if you're going to be manipulating the data w/ heavy complex analysis as well as a ton of data-points, it should occur not on the prod db.

I was referring to queries such as: User needs to get a list of pharmacies they've gone to in the past 2 months that carries x-medication. Not overly complex, but annoyingly more code that would have to be written + architected in NoSQL vs a relational db.

That's when having mongodb+RDBMS with the added complexity is really justified. On common cases, just drop mongodb and use the RDBMS for everything.