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From the qt docs:

"The Gooch lighting model uses both color and brightness to help show the
curvature of 3D surfaces. This is often better than models such as Phong
that rely purely upon changes in brightness. In situations such as in CAD
and CAM applications where photorealism is not a goal, the Gooch shading
model in conjunction with some kind of silhouette edge inking is a popular
solution.

The Gooch lighting model is explained fully in the original Gooch paper.
The Gooch model mixes a diffuse object color with a user-provided cool
color and warm color to produce the end points of a color ramp that is
used to shade the object based upon the cosine of the angle between the
vector from the fragment to the light source and the fragment's normal
vector. Optionally, a specular highlight can be added on top. The
relative contributions to the cool and warm colors by the diffuse color
are controlled by the alpha and beta properties respecitvely."""

The TLDR: the shader works well for revealing 3d details of objects
which may otherwise be hidden due to the scene's lighting. Ultimately,
it's an easier material to work with as you don't need to worry
about setting up appropriate scene lighting in order to visualise features.