I've got a project where one part of the application is just for editing a medium-sized, hierarchical object. So it's easiest to just get it from the database as a whole, and update it like that. It's also very easy to understand for the frontend programmers. The other part gets data from users and dumps it in its entirety in another table. Then the analysis part simply retrieves them all (at most a few thousand objects), and can build graphs, or whatever visualization with them. There's not a single JOIN involved, and updating is simple. If it goes beyond that, it's time to look at a relational database, either for performance reasons or because the API becomes cumbersome.