I used to make smoothies with the whole vegetable/fruit. It really was quite nice. My combo featured cucumber, soybean milk (or other nut milks), apple, banana, and various other ingredients. Since it was a smoothie, it had the full fiber content of the ingredients, not just the juice.
It was actually quite filling if adding quinoa, oats or other grains. I think I used additional fiber, too. I really enjoy the green smoothies, but my wife thought they were ‘odd’.