A heat pump warms a home more efficiently than using the same amount of electricity for resistive heating. It can do this because it's not generating the heat from scratch; it's moving heat from outside to inside.
Thank you for helping me learn a new HVAC term!
It's desirable for multiple reasons, of course, but it's not efficiency.
The 400% metric let's you compare with other heaters, the 100% is kind of useless.