long as loads placed on a circuit are within the range it was designed for, 120 V is more than good enough to run most appliances. The Japanese have done extremely well on their 100 V system. Larger equipment that run more efficiently on higher voltages like water heaters, clothes dryers and air conditioners are plugged into dedicated circuits with dedicated plugs and outlets (you can look up the NEMA connector standards if you want to know more). For smaller appliances that have a heating element like kettles and frying pans the difference in output really doesn’t make a difference to most people; they heat up as much as needed in a reasonable amount of time, waiting a couple more minutes is not a big deal. For vacuum cleaners it matters even less, they start up just as fast and vacuum just as well.