Meet Sjarn - proxy
Storyboards are drawn to get a visual impression of how the story evolves.It isn't always created, but it mostly is for animation movies. What you don't get an impression of in storyboards, is timing. How lang does it take to get a character to drink a glass of water, or how long does it take to walk up the stairs? Such actions can be tested by filming with a camera, but there are actions we never perform. We don't fly, we don't swim as dolphins, we don't use magical weapons to shoot lightning bolts to our enemies. Apart from that, actions can be performed faster or slower, depending on the context. When we're in a hurry we'll be faster for example, or slower, when we're relaxed.
Tempo and rhythm can be tested by filming in regular filmed movies. With animation things get quite different. There has to be a scene, and the entire scene needs to be animated to see if it's right. It's a bit too much work when the final, detailed characters and 3D-models are used. Animating 3D is similar to working with puppets. When using advanced puppets you'll have to control a lot of strings to get the right motion. When using simplified versions, the animation can be made faster to test how it looks.
That's why 'proxies', simplified characters are used that can be animated much faster. That way we can get an impression of how the animated character will look like, and we can test several versions of the animation. That's why we now have 'Sjarn-proxy'.
A second reason is of an aesthetic nature. When creating animatics with finished characters there's a constant feeling of having to improve the pose to make it look right, while the poses don't have to be perfect yet. With a basic puppet that 'need to add detail' is absent. It makes it easier for us to focus on what has to be done.