It depends which plants they are Nellie as they differ. If you can say which you are interested in we can advise you better.

It depends on he plant/shrub as to whether they need pruning!

and of course in the wild there is no pruning. we chose to prune to maintain the shape/flowering/vigour of a plant.

I often prune to keep the plant with in bounds in the space it is in.

In the ideal naturalistic landscape, plants that only grow the proper size for their role are selected, so that future pruning needs are minimal. Since such landscapes can look pretty bare for the first few years, and designers rarely think beyond the first five years, things rarely work out so well. So lots of landscapes need regular pruning to keep from becoming impassable thickets. Also, formal landscapes are built around absolute control of nature, so they usually require frequent cutting back to keep everything in its artificial shape and place. Probably most landscapes contain elements of both styles, along with their pruning needs.

No, not 'necessary' at all. Shrub pruning (which is what I assume you're talking about) is generally done to limit size and shape. If you don't want to do it, because you have the room for shrubs to reach their eventual size, then don't do it. Just let them grow and do their thing.

Bearing in mind that some people refer to cutting back perennials as pruning it would be useful to know which particular plants you are talking about though.

Think of all the truly massive formal Yew or Beech hedges on estates or older public gardens. They are cut back at least every year, but they have still grown to huge--even absurd--size

Come to think of it they do have the ambition to be big trees...