Function calling gives the model a controlled way to take action. Instead of generating loose text and hoping another system understands it, the model outputs a structured request such as "create lead," "summarize ticket," "send email draft," or "query customer record" with the required fields.
For Growth Marshal's audience, function calling is plumbing, but it is important plumbing. It makes agent behavior more predictable, testable, and secure. It is one of the mechanisms that turns natural-language reasoning into real software actions.