Too many cooks, or too many robots? Finding a Goldilocks level of randomness to keep robot swarms moving

Picture a futuristic swarm of robots deployed on a time-sensitive task, like cleaning up an oil spill or assembling a machine. At first, adding robots is advantageous, since many hands make light work. But a tipping point comes when too many crowd the space, getting in each other's way and slowing the whole task down.