Inverter incorporates feedbacks from your environment so that your machine does not work at a constant speed all the time!

It helps when the kW/h usage is high, eg air cond, it slows down the speed of the motor when the room temperature cools down sufficiently till the target temperature, and ramps its up again when it dips down abit, instead of all the time working hard.

For factories we use them in larger motors for cost efficiency, so yes, it helps. But you have to use them enough to see the difference.

Just compare the kW/h specs you can make a comparison.