A fridge moves a certain amount of heat energy from the inside to the outside, but that doesn't come for free. You have to put extra energy into the system to make that happen. The hot side of the fridge gets the "moved" heat plus the heat from the work you had to do to move the heat. The work heat is waste.
If what you're trying to do is make something hot, you're moving heat energy from the outside to where you want it to be hot. That makes it hotter, but it requires work. In this case, since you want to make things hot anyway, that work heat is extra bonus heat.
A fridge moves a certain amount of heat energy from the inside to the outside, but that doesn't come for free. You have to put extra energy into the system to make that happen. The hot side of the fridge gets the "moved" heat plus the heat from the work you had to do to move the heat. The work heat is waste.
If what you're trying to do is make something hot, you're moving heat energy from the outside to where you want it to be hot. That makes it hotter, but it requires work. In this case, since you want to make things hot anyway, that work heat is extra bonus heat.