Putting it quite brutally, abridged audiobooks are butchered versions of the authors work. Often removing the flesh and just leaving the bare bones of the story behind. Some people do prefer abridged versions as they can get through a book in a relatively short time, for instance in a single train journey or a simple commute into London and back.
Unabridged versions are the story as the author intended and had wrote, allowing the reader/listener the opportunity to luxuriate in the depth of the story and fully enjoy the experience of having an entire bookread from cover to cover for their pleasure.