Our company uses a mix of both. The author mentions that one of the perceived benefits is the "Flexibility of schema definition". We actually ended up needing a

Our company uses a mix of both. The author mentions that one of the perceived benefits is the "Flexibility of schema definition". We actually ended up needing a NoSQL database for exactly that. We have one part of our system that needed to store schema-less data in a way that still let us query it using the custom data fields. I wish we could have found a way to make it work within our SQL database but none of the solutions that I could find felt right. Schema-less data and complex queries (Group Bys, Distinct, etc) just don't seem to mix well with most systems. I'd love to know if others have any experience in this area.