Not having human input in the loop, i.e. allowing agents to act without guidance. I understand the idea of having agents guide agents, but really how much do we gain when Sol scolds Fable?
You might be surprised at how much benefit you get from the model council[0] pattern.
The common pattern I've seen is "build with Claude, review with GPT", or vice-versa.
It's been proven to be very effective.
0: https://www.google.com/search?q=model+council+pattern&udm=14