Copilot didn't charge for subagents. You could do an insane amount of work with dozens of subagents with a single request and a deep enough prompt to kick it off.

I setup entire virtual teams (Dev, QA, product, reviewers etc with the initiating model just acting as the agent manager to keep it's context minimal) to one-shot some stuff and it kept churning and making progress.

Those days are just about over with the change to token pricing but for a time....