In many cases there are specific trees, shrubs, etc. that will require very little pruning. A good example of this is my Dwarf Colorado Intense Blue Spruce. This wonderful tree has been thriving for ten years and the number of times I have pruned it can be counted on one hand. When there is a visible problem or an unusually strange looking branch I will lightly prune to correct the problem. Aside from that I let nature takes it's course. In my opinion these specimens are simply magnificent in their natural state.
To illustrate the before and after I took pictures of an evergreen while pruning. The front view shows the bottom clipped and the top left in a natural state. The side view clearly defines the difference of the new width and the smooth appearance of the clipped bottom.
One evening while I was visiting garden sites on the internet, something quite humorous occurred. One gardening page was emphatic about pruning. This person described pruning all species and explained that if left unattended they have a tendency to look spindly, unkempt and in summation just awful. Immediately after leaving that site the next webpage had a heading that read something like this: Take those darn garden shears and throw them out. This person was a strong advocate of allowing each and every plant to attain it's own shape and individuality and mentioned that their garden was unique and healthy. In essence many of the shapes and designs are personal choice. The best idea is to design an area, choose your favorite plants and maintain to your liking.
My personal preference is to prune but not severely. I find a variety of pleasing shapes appealing and the only instance for radical pruning is to save a specimen. It is important to maintain pruning equipment by keeping the blades sharp.