What is this "ArcBall" in the Bundled script that comes along with Armory?

I tried it on a cube and when I click play Camera = “Viewport” & drag around the camera seems to rotate up down left right and the cube also rotate INVERSE of that.
What is the point of this ArcBall thing ?
Am I using it correctly ?
What is this used for ?

an example of use can be seen here