It is nearly impossible to eliminate all shadowing in a photograph.
As a general rule of thumb, especially when shooting portrait photos, soft shadows are acceptable and can enhance an image while harder shadows tend to have a negative effect. This is typically the case, but not always.
Take for example the images below:
The first is a sample of a photo with harsh shadows and the second is one with a softer shadowing effect.
However, in some cases a unique use of dark shadows can add for a wonderful aesthetic fell.
See the following images for as examples:
The first is an amazing shot by a talented photography names Hannah Wessman. The second is a shot I took which is published in my second or two poetry books along with one of my poems.
What lesson can we take from this? While there are rules in photography as in any art form, sometimes they can be bent or even broken and produce an amazing finished product.