I wrote some software at an automated trading firm that would do the subset of "parsing ticks and maintaining order books" sufficient to map ticks to symbols, and no more work than that. My code was pinned to one core and spun waiting for an expensive network card to DMA some ticks into memory, then when ticks we cared about were found it would load them onto one or more queues. Each queue corresponded to a different thread spin waiting on its own pinned core.
So one use case is "transforming ticks into trading decisions slightly faster than you otherwise could"
Software industrial process control, such as motors and let robotics. The longer latencies make the control loop less responsive or unstable. Microseconds granularity is very useful there.
a friend of mine recently told me how Windows schedules cpu-bound threads to different cores to prevent thermal throttling, so I now wonder if we were mucking things up by running our CPUs too hot
If you weren't pegging thermal max you shouldn't be seeing thermal limiting. Although you're probably right that cooling is something software people are more likely overlook than SRE/hardware/lab folks.
Essentialy any true HPC workload. You can go pretty far by ignoring latency and doing some series of map and reduce stages on top of giant conceptual file with large-ish records. There are workloads where data for these partial parallel jobs are on the order of machine word or two and then you really care about communication latency between cores.
I wrote some software at an automated trading firm that would do the subset of "parsing ticks and maintaining order books" sufficient to map ticks to symbols, and no more work than that. My code was pinned to one core and spun waiting for an expensive network card to DMA some ticks into memory, then when ticks we cared about were found it would load them onto one or more queues. Each queue corresponded to a different thread spin waiting on its own pinned core.
So one use case is "transforming ticks into trading decisions slightly faster than you otherwise could"