Since appliance ratings (in watts) are much the same everywhere in the world, it makes for a much lower (roughly half) instantaneous current load throughout the (relatively) low-voltage portions of a reticulation system to deliver the required wattage at 240V than it does at 120V. That's the simple base for LCGuy's observation.

Long-distance transmission of AC at thousands of kilovolts is the practice for the same reason. Cables can be lighter, and therefore cheaper, for a given wattage delivered.

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