I find that JSON(B) works best when you have a collection of data with different or variant concrete types of data that aren't 1:1 matches. Ex: the actual transaction result if you have different payment processors (paypal, amazon, google, apple-pay, etc)... you don't necessarily want/care about having N different tables for a clean mapping (along with the overhead of a join) to pull the transaction details in the original format(s).

Another example is a classifieds website, where your extra details for a Dress are going to be quite a bit different than the details for a Car or Watch. But, again, you don't necessarily want to inflate the table structure for a fully normalized flow.

If you're using a concretely typed service language it can help. C# does a decent job here. But even then, mixing in Zod with Hono and OpenAPI isn't exactly difficult on the JS/TS front.