The use-case for a more efficient JSON parser is exactly the same as the use-case for a less efficient one. They're doing the same thing. Daniel Lemire does a

The use-case for a more efficient JSON parser is exactly the same as the use-case for a less efficient one. They're doing the same thing. Daniel Lemire does a ton of performance research like this. He's an unusual case of a professor who publishes fully working source code. There's a good chance that your database of choice uses some of his stuff or was influenced by his research.