It means heating/cooling many buildings rather than a few, many individuals cooking alone etc.
It seems it is better in the USA [1] and the UK [2] though there is considerable variance when comparing several European countries [3].
[1] https://www.scientificamerican.com/article/working-remotely-...
[2] https://circularecology.com/news/the-carbon-emissions-of-hom...
[3] https://www.vodafone-institut.de/wp-content/uploads/2021/06/...
A newer system can have different temperatures. I'm in a cold climate, but when my heating is "off" it's actually set to heat if the temperature falls below 8°C. (Probably it should be higher, but it's an apartment surrounded by others, so the temperature will never fall that low anyway.)
These factors are probably why there's significant variation within European countries.
[1] https://www.wolseley.co.uk/product/danfoss-randall-3020p-24-...
My understanding is that the annual kWh energy consumption of a heat pump will be slightly greater that an electric vehicle. But most two-adult families each have their own car, doubling the energy demand. It also require a lot more energy to build an electric vehicle than a heat pump, and requires more scarce minerals - with their own security and environmental problems. But then if people commute by walking, cycling or train, that's a very different calculation.
Or the large scale logistics to service, maintain, supply, and feed these metropolis': it's a centralized relic of a bygone era, and the sooner we accelerate WFH and actually frame it as way to counter-act climate change this will never gain traction. Succumbing to the landed gentry's will has been a story as old as feudalism itself, but this has to be something that must be collectively fought for.
I've lived in commercial buildings in a city cental, and at night or on Sundays when I was there entirely on my own all the heaters/ac heat pumps would still be going all day/night: and all the lighting and electronic devices plugged in were still whirring away. I got really drunk one night and lost my keys walking up the stairs (the elevator was still on just not accessible from my side of the building at night) and while trying to retrace my steps I realized how deafening how the sound of so many devices can be if you actually pay attention to it with no other ambient/background noise is there to mute it.