Windows certainly wastes a lot of time doing background registry scans and Metro (Win8 mode) style apps collecting updates for all the mobile like apps. news, photos weather, pictures, mail etc , while you think nothing is happening. Win 10 is supposed to merge these two environments. Metro insists on UAC enabled, while I run with it off like XP mode and prefer to control my environment and choose my own 3rd party apps. Who knows maybe it runs as smooth as mobile phone in single tasking mode except multitasking on Quad core with 8GB but consuming no more than 1/4 of all CPU's per application.
I still use Windows Media Centre for OTA TV from router based TV tuner, so no Win 10 for me as this is not offered for now. But then we watch more recorded media now TV and new SD & HD movies free using web based KODI which runs on almost anything..