Do you have some very large electric motors? Grinding and milling machines, car crushers?
It will have no effect on use of electricity for heating, including immersion heaters, washing machines, tumble driers and ovens. Most domestic electricity is used on heating.
Are you using a lot of incandescent (filament) light bulbs? It will make them burn a little dimmer and last a little longer. It will not affect CFL (energy saving bulbs)
When the DNO was testing the supply at my domestic premises recently, I was surprised to find it had already been reduced from the old UK standard of 240v/415v to 220v/405v.