There have been a ton of start-ups that I've talked to / been a part of who used MongoDb thinking their company is going to exponentially explode in MAU and they think they'll save themselves the scaling troubles by using NoSQL. What ends up happening is the codebase gets too gnarly when they try to start doing complex analysis. SQL is appropriate for like 95% of companies. A lot of these places I'm referencing end up porting their codebase to Postgres, mysql or oracle.