I think everyone forms their opinion on this subject based on their own subjective experience. If you live in a heat trap then air con is highly useful - it is currently 23C in here, which is somewhat uncomfortably warm to sleep in for me and in warmer conditions it just plain too hot.
Building thermal efficiency, personal comfort requirements, and current weather conditions combine to produce different results case by case.
I could present an argument that central heating is a waste as it's only really needed about 15% of the year...for me, but the next person might need it a lot more to have the same comfort level.
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The thermostat hasn't had much action here yet, but it's all ready to go to make me too hot again as deemed necessary.