Ask HN: Tool Calls vs. Structured Responses

Hi, I feel like everyone is building LLM Agents (and Agent frameworks) recently and I would like to know what approaches people prefer when building these:

* Tool Calls - give the LLM the tools and let it figure out the details

* Structured responses - ask the LLM to give you all the details in one shot

I can imagine that each approach has specific use cases (and "combination of both" is likely the correct answer).

Yet - what are people's experiences with building agents using the two approaches and which should be used when?

Any links to research on the topic would be appreciated (including pervious HN discussions on the topic if any).