That was the most common principle used in dual+ core smartphones as cores shut down once they're done, which made it more efficient to run them at full speed t

That was the most common principle used in dual+ core smartphones as cores shut down once they're done, which made it more efficient to run them at full speed then shut down (within limits; the difference in power consumption between 2GHz and 1.4GHz is negligible, but the performance is noticeable). Of course, laptop and desktop CPUs got that feature as well, so that idea still holds true today. It's kind of like Auto stop/start on engines - saves more fuel than it wastes.