As one of the previous posters mentioned the Invertor controls the Motor speed by changing the frequency of the Electricity and sometimes even the waveform from sinusoidal to sawtooth or other, this is known as "Variable Speed Control" it does make things more efficient.
People who travel on electric trains will hear the noise changing tone/frequency as the train excelerates, a similar thing is happening with your Refrigerator, Aircon, washing machine, but we can't hear it in the same manner.
Electricity at 50hz can only drive a motor wound with a fix amount of Poles at a set speed, previously to make the motor go quickly or have more Torque there was other tricks, but now there is the Invertor which can increase the Frequency of the Electricity, which increases or slows the Motor Speed.
But this is Thailand, there are many Lightening Strikes every month, this send Spikes through the supply network 3 or 4 times the magnitude of the 230vAC supply you only might see a dip in the lights a Brown Out which can damage delicate electronics, hi tec is not always reliable, who is going to fix it, in our through away society
Even in the UK we have this issue l am now on my 3rd Solar Inverter in 10 Years.
In my opion the efficiency benefits for most domestic electrical device are negligible, unless you want a Washing machine that spins your clothes at 200rpm