More flexible, and (evaluating non-scientifically!) qualitatively better answers & instruction following -- particularly for deeply nested or complex schemas, which typescript expresses very clearly and succinctly.
Example from a hack week project earlier this month (using a TS-ish schema description that's copy/pasted from healthcare's FHIR standard): https://github.com/microsoft-healthcare-madison/hackweek-202...
Or a more complex example with one model call to invent a TS schema on-the-fly and another call to abstract clinical data into it: https://github.com/microsoft-healthcare-madison/hackweek-202...
The docs say it's on by default if you use function calling normally: https://platform.openai.com/docs/guides/text-generation/json...
> Note that JSON mode is always enabled when the model is generating arguments as part of function calling.