Model sheets depict characters in their front view, side view, behind, and facial expressions, etc. In anime production animators use these, but what does it contribute in trying to animate?
Like I already guessed in the comments, model sheets are used to guarantee consistency in character design.
They are a concept art to define the character design. In big teams, you have the problem that everyone sees the character a bit different, so they try to standardize the design by creating a model.