[k__]

Really?

I had the feeling that data-models of document stores like MongoDB often only fit one use-case and fail after that.

A blog, for example.

You have Article and Comment and when using a document store, it comes naturally to embed Comment in Article, because, well the first thing you need is to display comments below articles.

Then you want to show the comments of a user, but they are stored inside the articles...

If you had a relational data-store the way to retrieve the data for both cases would be the same mechanism, a join.