I was checking a question today and saw it with the cpu and wondering exactly how it should be used I read the excerpt which basically told me what a CPU is, not what the tag is useful for. Now, checking the questions I see several questions about monitoring the cpu, cpu usage, cpu temperature, where the only thing in common is that the questions have something related with the CPU, but I do not see how that could be useful for this site. Is there any intended use that I'm not seeing? What should be the tag excerpt/wiki?
There is nothing more to it actually. The CPU tag is for CPU related questions.
The CPU is the piece of hardware executing instructions, therefore subjects can be related to the CPU in different ways. One can ask about performance while the other about intel x86 architecture, both are CPU related.
To your question - programmers writing low-level code, security researchers, performance engineers are just a few examples of people might be interested in CPU related questions.