> I've written this before: if your data looks like trees, with some loose coupling between them, it's a good choice. And most data does look like trees.

I had an education statup a little while ago.

Courses had many cohorts, cohorts had many sessions.

It really was much nicer having a single tree structure for each course, appending new cohorts etc, rather than trying to represent this in a flat Postgres database.

That said I acknowledge and agree with other commenter's experiences about MongoDB and data loss in the past.