Contrast

Narrow beam angles create high contrasts in the visual environment. If the ceiling and walls are not lit at all, a cavern effect can be created which will create an unpleasant feeling.
Broader distributions of the fittings will create a visually interesting scalloping pattern on the walls while still casting shadows which result in a good contrast.
Very diffuse light creates uniformly lit surfaces. Since no shadows are cast, it can be difficult to recognise objects.

Ambience and modelling changes as beam angle widens

(All images courtesy of Marlin Lighting)