Why would you need to know about each processor in particular?
I'm curious to understand what could be the motivation behind the fine-grained detail of each virtual processor that the Windows 8 task manager seems to be focusing on.
Here's a screenshot (from here):
I know this setup could only exist in a non-standard, costly, important server environment (1TB RAM!), but what is the use of a heatmap? Or, setting processor affinity:
What I'm asking is, under what circumstances a developer would care if specific processor X is being used more than processor Y (instead of just knowing that a single non-multithreaded process is maxing out a core, which would be better shown as a process heatmap, instead of a processor heatmap), or care whether a process will use this or that processor (which I can't expect a human to guess better than an auto-balancing algorithm)?
In most cases, it doesn't matter, and the heatmap does nothing more than look cool.
Big servers, though, are different. Some processors have a "NUMA", or Non-Uniform Memory Access, architecture. In these cases, some processor cores are able to access some chunks of memory faster than other cores. In these cases, adjusting the process affinity to keep the process on the cores with faster memory access might prove useful. Also, if a processor has per-core caches (as many do), there might be a performance cost if a thread were to jump from one core to another. The Windows scheduler should do a good job avoiding switches like these, but I could imagine in some strange workloads you might need to force it.
These settings could also be useful if you want to limit the number of cores an application is using (say to keep some other cores free for another dedicated task.) It might also be useful if you're running a stress test and you are trying to determine if you have a bad CPU core. It also could work around BIOS/firmware bugs such as the bugs related to high-performance timers that plagued many multi-core CPUs from a few years back.