In general, gear drive is useful for power transmission between two shafts, which are near to each other (at most at 1m distance). In addition, it has maximum efficiency while transmitting power. It is durable compare to other such as belts chain drives etc. You can change the power to speed ratio.

Advantages: -

It is used to get various speeds in different load conditions.

It increases fuel efficiency.

Increases engine efficiency.

Need less power input when operated manually.