Someone more knowledgeable than me needs to give a proper answer but I didn't think there was an actual reserve on the PC and the app has full access to the CPU if it needs it (and nothing else is running of course). I thought the whole point of the console reserve was to allow predictable performance for both games and apps which the PC doesn't really have.
Right but say that voice chat is handled by the OS-side CPUs on the consoles, voice chat still has to be handled on the PC as well, etc.