There's a team at my company that chose Mongo for a new data transform project about a year ago. They didn't create a schema for their output (haven't to this day) and I'm convinced they chose it purely because they could just not handle any edge cases and hope nobody would notice until it was already deployed, which is what happened. For example maybe one in a thousand of the records are just error messages - like they were calling an API and got rate limited or a 404 or whatever and just took that response and shoved it into the collection with everything else.