This is getting more complicated than it needs to, basically, when using a higher voltage, it takes less current to produce the same amount of power (watts) than when using a lower voltage. Higher voltages are used on transmission lines to reduce the voltage drop on the line, caused by the resistance and power loss of the line. This allows us to use smaller conductors on power lines. If the voltages were lower, we would need to use larger conductors (less resistance) to have the same voltage (or slightly lower) available on the other end.