I have the Ronin SC and i notice that the focus wheel helps to adjust the focus of the camera when connected to the ronin through USB C.

So what exactly is the focus motor for in this regard?

I understand that we can use it for the zoom but in such cases i wont be able to focus the lens through ronin.

There are two things, where you need to use it, first would be manual lenses, second would be where you can't focus through the camera with the focus wheel. And there's also lenses which allow you to directly set the focus instead of by wire, in that case you can use the motor to gain finer control depending on the camera.