Adjacent data that is very alike for most usage but different in subtle ways.
Classified ads, the additional details for a Car are different than a Shirt, but both would be ads. And adding a nearly infinite number of fields or a flexible system in a set of schema or detail tables is significantly worse than unstructured JSON.
Another would be records from different, but related systems. Such as the transaction details for an order payment. Paypal data will be different from your CC processor, or debit transaction, but you can just store it as additional details for a given "payment" record.
Another still would be in healthcare, or any number of other systems where the structures will be different from one system to another depending on data interchange, where in the storage you don't care too much, only in the application layer will it make any necessary difference.
Classified ads, the additional details for a Car are different than a Shirt, but both would be ads. And adding a nearly infinite number of fields or a flexible system in a set of schema or detail tables is significantly worse than unstructured JSON.
Another would be records from different, but related systems. Such as the transaction details for an order payment. Paypal data will be different from your CC processor, or debit transaction, but you can just store it as additional details for a given "payment" record.
Another still would be in healthcare, or any number of other systems where the structures will be different from one system to another depending on data interchange, where in the storage you don't care too much, only in the application layer will it make any necessary difference.