I disagree with the assertion that the main advantage of relational databases is to save disk space.<p>The main advantage of the relational model, as with any solid method of abstraction, is to save developer time and enable stronger use cases by providing a provably correct way of reasoning about data (predicate logic, relational calculus, etc.), which you do not get with NoSQL.<p>Unlike, say, functional programming, it's also quite easy to teach the relational model properly to complete beginners (like non-technical finance department staff) in a matter of days or weeks, which makes it a uniquely high ROI paradigm to add to your company.<p>I strongly recommend reading through at least the latest book by either Edgar Codd or Christopher Date.