It is tempting to skip storyboards when video is a click away. Do not. The storyboard is the cheapest place to be wrong.
Composition is a decision
Where the character stands, how much sky there is, whether we are close or far: these choices define the scene more than the rendering quality does. A storyboard frame lets you make them for a few thousand tokens instead of hundreds of thousands.
Continuity lives here
Line up your frames and you see the film's rhythm: too many wide shots, a missing reaction, a jump in lighting. Fixing that at frame level is a regeneration; fixing it at video level is a reshoot.
Frames become anchors
A frame you approve becomes the first frame of the clip. That is the single most effective way to get the video you imagined: the model starts from your picture, not from a description of it.
Practical rule
Storyboard every scene on the draft tier. Move to standard only for frames you will anchor a video on.