Pixar used storyboarding right from the beginning. They use it as a plan to show the characters and the story. First, they started with hand drawn storyboards. They continue this until the story is fully developed. After that they take it to the computer. They start to animate it. They add color and detail. Next they add the audio. The audio must sync with the animation. Finally the film is complete. With this processes, you are able to plan everything out before bringing it on screen.
In this link, they show how their storyboard looks when you take it to a computer.