OK, this is actually my own answer to an unwritten question on this title problem chasen today ...
Why there is WUDFHost.exe constantly on some 12-20% CPU?
According to several posts on the net "The WUDFHost.exe process is part of Windows Driver Foundation of Microsoft", and an essential one, if found on %WinDir%\System32 folder. It is pointed to be taking care of "User-mode Drivers".
After checking the drivers on this about half-year old laptop, first 3 most critical ones manually and also updating them, I didn't still note any change on the CPU list. Then I went on checking others automatically this time with the Free Driver Booster 3, and it found some 12 more drivers outdated. So, now I let twice some 3-4 "easy" ones get updated automatically by DB3 and there between checked the actual CPU list, but still no change. But, after an automatic DB3 update of the last "critical/difficult" 5 m/b drivers the WUDFHost.exe was on 0% CPU, great! Note also, that all of the updated 15 drivers were just 3-12 months old.
Edit 18.08.2016 10:30 (GMT+3):
Sorry, to inform, but this cure was a short joy, after Windows 10 was Upgraded from 1511 to 1607 the problem did return, i.e. back to 15-17% CPU, and now the DB3 did recognise only up-to-date drivers ... See below my comments on this.
Edit 18.08.2016 12:30 (GMT+3):
OK, the new troublemaker identified -> Lenovo Quick Optimizer, see below my comment on it, and now this case hopefully finally cleared.