For simple tasks that require a lot of input tokens (e.g, "Figure out the full path this function calls through and give me a map", or "Summarize these 5 PDFs and give me the main ideas I should explore") you can fire off a Sonnet agent at low-mid reasoning at it'll be cheaper than if you had Opus do that summarization itself.
Now imagine you have a set of twenty of those tasks. You launch an Opus agent, give it the task list, and tell it not to do the work itself, but orchestrate agents to perform all of the tasks and do small spot checks to verify the work.
The overall task is completed much faster at a similar or cheaper cost with an extra verification layer inserted that wouldn't have been there if you just used Opus.
Now imagine you have a set of twenty of those tasks. You launch an Opus agent, give it the task list, and tell it not to do the work itself, but orchestrate agents to perform all of the tasks and do small spot checks to verify the work.
The overall task is completed much faster at a similar or cheaper cost with an extra verification layer inserted that wouldn't have been there if you just used Opus.