[MagicWishMonkey]

Depends on the app. My previous job required processing thousands of address book contact records uploaded to the server in a massive list. It was not unsual for some of these objects to exceed 10mb (when serialized to disk).

The default json module took close to 5 seconds to deserialize the payload once it hit the server, while ujson could do the same work in a fraction of the time (less than a second). 5 seconds might not seem like a whole lot when the import process as a whole could take 30 seconds or so, but when the user is stuck staring at their device it makes sense to cut down the response time any way you can.