I like to repeat some of Roddenberry's words:
The Starship Enterprise is not a collection of motion picture sets or a model used in visual effects. It is a very real vehicle; one designed for story-telling.
You, the audience, furnish its propulsion. With a wonderous leap of imagination, you make it into a real spaceship that can take us into the far reaches of the galaxy and sometimes even the depths of the human soul.
The purpose of all this? To show humans as we really are.