The logic of this has me intrigued and annoyed. It's one of these things invented by beaureaucrats who don't understand what they're on about, but gives them a warm fuzzy feeling inside.
For one thing, the theory may work at face value with a 230V supply and 240V appliances, but what happens further down the track when the old 240V appliances are out of service and there's only new 230V ones? Reduce the supply then to 220V?
Secondly, this theory only applies to certain loads, I don't see a switchmode power supply for example reducing its power consumption on reduced voltage.
Then we have the situation with some heating appliances, say an oven. To get to the same temperature that it did at 240V, the element will have to stay on for a longer period when the supply is 230V.
Thankfully, the politically correct powers haven't got this far in Australia and I'm happy to report the phase voltage still measures 240-250.
It's a sore point with me having once lived at the end of the line and only getting 180-220V. I had to plug the TV into a variac just for starters...
