Some of it can be busywork, but for me the intermediate artifacts (plans, design docs, etc) serve a real purpose: they create a verification surface where you can check that the agent is creating the right thing before it goes all the way. It's exactly the same reason we created short sprints: if the team misunderstood the requirements and built the wrong thing, you only lost a sprint. We lost months of work when we did waterfall because the product did not match what the customer had in mind.
I have deterministic and stochastic tests that run on each artifact. For those that have a high risk of "not the right thing", I manually review the artifacts. But if it's bog standard I just rely on the auto-gates to reject and get the agent to retry the artifact.
This gets me a high-volume pipeline that yes uses a lot of tokens, but at the same time doesn't overwhelm me. I only deal with things that genuinely need my attention. That's worth it for me, and not busywork.