Hibernation for New Horizons means the science instruments are turned off, the high gain antenna is pointed toward Earth, the spacecraft computer system is put in a low power mode, and the thrusters are fired to put the spacecraft into a gentle spin. The instruments are turned off to save wear and tear on the electronics. The spin helps the spacecraft maintain course.
MD, who worked on the Alice instrument on New Horizons
Ah. Well the article said “to preserve its energy”, and you don’t know my knack for nit-picking. Spinning doesn’t help maintain its course, by the way, it helps maintain its attitude.