You can do a basic google search, and you will find out use cases where document-based data storages are advantageous compare to relational ones.
I'm a Domain Driven Design true believer. The thought of just being able to store my entire domain model without the machinations of the object relational impedance mismatches was glorious.
I use C# so my document collections are strongly typed C# objects and thanks to the Mongo C# Linq provider, my queries are also strongly typed.
It is always just the display data on details page
Not sure if thats a good use case, but it cleaned up our tables and given the data fields can vary from customer to customer its a nice flexibility. Previously it was an Entity-attribute-value setup for these fields (which was very slow after we got into millions of rows) and we were considering a NoSQL option
https://www.postgresql.org/docs/10/static/datatype-json.html