Half of all primary energy usage is for heating purposes. Heat is the best format to displace, as well, since a significant chunk of all that primary energy use is direct fossil fuel combustion right now.

Especially since you can use heat to drive a heat pump, which ends up actually achieving above unity efficiency effectively since the heat input is used to move additional heat from the environment. Even if it's inefficient, if the heat would otherwise have been wasted, it's a net benefit.