NoSQL is good when you want speed, and thus denormalized data is its motto, as NoSQL is used to store documents, not entities we are used to have in RDBMS. Whenever you need to normalize and dedupe your data, RDBMS is a must.
NoSQL techs generally support referencing, but they are performance-prohibitive: thus referencing is very rarely used with docs.
Overall: NoSQL = denormalized, duped data for fast retrieval, think of it as middleware of data storing SQL = normalized, deduped data storage where your real data is stored for long-term; think of it as REAL data-source
So, best way to go is to use both, according to their purpose.