[krisoft]

> This is completely unnecessary, you only need to pick the lens that you actually want.

It sounds like you are thinking only in the context of photography. In robotics and machine vision applications you often choose the fisheye lens because they are cheaper than the rectilinear lenses with the same FOV. (if a rectilinear lens is even available in the form factor and FOV you need.)

So what people do in those situations is that they get a crappier lens and they calibrate it so the algorithms know how much to correct for its crappyness. That is where this kind of calibration really shines.