They're just usually deployed for frozen warehouses, factories that actively freeze large amounts of (usually food), and AFAIK the occasional ice(hockey) rink.
Shitty types that don't even bother with any decent controls/pumps (those 90% boilers use a water loop circulation pump and a combustion air blower together with a bunch of sensors and valves) run propane-fired in many camper vans to do the fridge. But at the scale of an apartment building fit for 50+ residents, a natural gas fired central heat pump can be _quite_ efficient and economical.
Thermodynamically they're a heat engine with high combustion/flame temperature that uses the warm side as the heat sink, mated to a heat pump that consumes the produced "mechanical/electrical grade" power to pump heat from the cold side to _also_ the warm side. You save the turbine! Also the electrics but they're probably not even that expensive relative to the rest of the 200MW-class combined cycle natural gas power plant.