We often use 3d visualization to highlight specific landforms like ridgelines. When you view along the ridge axis, you can use lighting that's roughly perpendicular to the ridge axis to highlight. In this way, one side of the ridge is illuminated while the other is shaded.
It's more difficult to bring out a ridge when you're viewing a face straight on (perpendicular to the ridge axis). The whole face is usually either illuminated or shaded and it's hard to distinguish it from background landscape elements.
In the image above, I'd like to highlight the ridge in the center. Right now it blends in with the background terrain and is difficult to see.
Here's where attenuation comes in. I'll model clear air in front of the ridge and haze behind. Here's the result:
Now it really pops!