Schemaless database are a joy to use because they make it easy to iterate on your app, especially early on. The relational model isn't always the best fit for evolving and messy data in the real world. And let's be honest—it's painful to persist rich domain models across millions of little tables. However as your data model stabilizes, the lack of well-defined schemas becomes painful. On the other hand, relational databases are proven, robust, and powerful. How are we supposed to pick one or the other? Simple: pick both.