Earlier, the function of the resistor was to restrict the flow the electric - current. More is the resistance employed, lesser will be voltage and hence less will be the current flow. But in that way, the power - consumption could not be reduced since because of higher resistors, there was wastage of energy in the form of heat. In case of employment of less resistance, the entire current offered the maximum power to operate the fan in full speed.
So, we could conclude that speed - variation by applying different resistors provided the variable speed but the power consumption was constant in all the cases.
With the advent of new type of regulator in the market, the consumption of current is directly proportional to the speed of the fan and hence, lesser is the speed, lesser is the power - consumption.