I guess practically this will be the equivalent to function calling with a single tool. The AI splits out some payload that you presumably feed into whatever you do next. There are only 2 possible outcomes: can/cannot produce payload, which is equivalent to call/not call the next functionality.

With function/tool calling, you give it a list of tools with payload and the AI will select between them, or refuse, so there are more than 2 possible outcomes.

(I've never used any of these APIs, get that from just reading the docs)