[adonese]

Content negotiation is it just for taste or do you have some other reasons?

I find one good use case for them when a browser can make good use case with a SSE whilst another client just needs a regular _json_ response

[simonw]

I don't like how undiscoverable it is, and how it blocks browser-based debugging. I'd much rather be able to open an issue with a GET link to a stable representation, where possible.

Cloudflare doesn't support it for caching (more specific Cloudflare doesn't obey the Vary: cache header).