Throughput rises, plateaus, then falls as added workers increase contention and coherency cost.
Gunther's law, which extends Amdahl by adding a coherency term. It is why adding staff or servers past a point actively reduces throughput rather than merely failing to help.
In practice
- A support team of twelve resolves more per day than the same team at twenty, where every ticket now crosses two queues and a handover.
- A database given four more servers serves fewer requests, because each write must now be agreed with three more machines.