Finite dome light

Using the finite dome light lets you "project" parts of the 360 image to an imaginary deformed sphere, which in turn lets you change the height of the horizon of the HDRI. Sometimes when shooting a 360 HDRI image and want use the sky parts only, but you will also get a tree's or buildings covering parts of the horizon line this is one way of hiding(lowering the horizon in the camera frustum or reflections in a object(f.e car). This finite option is a way of getting a clean horizon when rendering with low camera angle.

The other case would be to get more correct reflections in a reflective object, let's say a car or bike for example, by default the HDRI in the dome light is infinite far away from you object and camera since it's a perfect sphere, using this option let's you squeeze the bottom of the "sphere" / the HDRI so that you get correct reflections of objects/ground in the reflective object. This is useful even if you build a 3D ground/environment, as it's let's you get more correct reflections/backplate.