I came across an interesting article trying to compare main features, pros and cons of two leading database engines from relational (MySQL) and non-relational world - MongoDB.
The article focuses on these two database technologies, but in fact it can be extended to the whole realms of RDBMS and NoSQL databases.
Certain aspects of both domains can be considered as advantages or disadvantages, depending on the point of view and particular business case. The flexibility of schema in MongoDB is appealing to teams who implement applications dealing with unstructured data. The strictness of schema definition required by relational databases can be beneficial when the application needs to ensure that the data quality meets certain requirements.
You will find yourself in trouble if you choose wrong data architecture - performance issues, scalability, data quality problems, outages are amongst things that await you.