True or false: the histogram for a well exposed image should return to zero on both ends. Perhaps true if you want to see detail throughout, but not if you want a dramatic composition. The human eye expects detail in well lit areas. But dark shadows can add a touch of intrigue or even mystery.
Detail is generally a good thing. That's why a lack of focus can ruin an image. That's why photographers lust after higher resolution cameras with an ever increasing numbers of megapixels. That's why they sometimes struggle with limited depth of field.
But detail can also be a distraction. An image should be about something. It should have a subject. And too much detail elsewhere in the scene can draw the viewers attention away from what you want them focusing on. Shadows hide. They conceal. Objects lost in shadow are automatically and clearly not the subject. Sometimes the darkness of those shadows can create the contrast to make what is your subject seem that much more vibrant by comparison.
A shadow can even become the subject of an image, an inky black shape breaking up an otherwise normal scene. I usually realize the potential of such situations only after exhausting the more obvious subjects, but I know at least one photographer who has made such images his main pursuit. A shadow with a recognizable shape can become an iconic stand-in for all possible subjects with that shape, elevating it become an almost mythical archetype. Photograph a person, and a viewer will be interested in their features. Photograph a silhouette of a person and the image becomes simplified to represent the everyman. Simple, graphic shapes created by shadows can create equally powerful images.
Back in the days of film, I used to love Fuji Velvia both for its rich, saturated color palette and for its deep shadows. Exposure latitude with Velvia was limited and fell off rapidly below the point you exposed for resulting in magnificently deep and dramatic shadows. Scenes with too much subject brightness range I wanted to retain with problematic with Velvia since it was impossible to keep too much with detail. Those shadows were there whether I wanted them or not.
With digital, every image can look like it was shot with whatever film I want, and after the fact rather than having to decide ahead of time what to load my camera with. Lightroom and Photoshop allow for such choices to be made in the digital darkroom rather than in the field. Yes, you can go overboard with such choices just as you can with pretty much anything and everything with digital. But when used with moderation a simple curves adjustment to deepen the shadows can work wonders with some images.
Sometimes shadows are better than detail. Sometimes a little clipping on the shadow end of a histogram is precisely what is called for.