CPUs enter and exit sleep on Android devices constantly. Back in 2007 on the MSM7201A we'd go to power-down sleep for any idle times of >50mS (nothing to schedule for the next 50mS). Run fast and go to sleep has always been the primary power policy.
That said there's plenty of lightweight threads and processes that are mostly IO or event bound, do very little compute, and will run in roughly the same time on a small core as a large core, but the small cores have a lower static power footprint (base cost to have them powered up at all), so big.little works out well there.
That said there's plenty of lightweight threads and processes that are mostly IO or event bound, do very little compute, and will run in roughly the same time on a small core as a large core, but the small cores have a lower static power footprint (base cost to have them powered up at all), so big.little works out well there.