* The data does not map well to database tables, e.g. when it's tree structures (of course that could be represented as many table rows too, but it's complicated and may be slower when you always need to operate on the whole tree anyway)
* your programming language has better types and programming facilities than SQL offers; for example in our Haskell+TypeScript code base, we can conveniently serialise large nested data structures with 100s of types into JSON, without having to think about how to represent those trees as tables.
* The data does not map well to database tables, e.g. when it's tree structures (of course that could be represented as many table rows too, but it's complicated and may be slower when you always need to operate on the whole tree anyway)
* your programming language has better types and programming facilities than SQL offers; for example in our Haskell+TypeScript code base, we can conveniently serialise large nested data structures with 100s of types into JSON, without having to think about how to represent those trees as tables.