I often think about huge, fancy cloud setups literally costing silly money to run, being replaced by a single beast of a machine powered by a modern, high core count CPU (say 48+), lots of RAM and lots of high performance enterprise-grade SSD storage.

The difference in throughput for local versus distributed orchestration would mainly come from serdes, networking, switching. Serdes can be substantial. Networking and switching has been aggressively offloaded from CPU through better hardware support.

Individual tasks would definitely have better latency, but I'd suspect the impact on throughput/CPU usage might be muted. Of course at the extremes (very small jobs, very large/complex objects being passed) you'd see big gains.

Essentially all, I would guess. But scheduling jobs and moving data in and out of a single big machine can become a huge bottleneck.