Polyvision was only used for the final reel of Napoleon, to create a climactic finale. Filming the whole story in Polyvision was impractical as Gance wished for a number of innovative shots, each requiring greater flexibility than was allowed by three interlocked cameras.
Polyvision was used only for the final sequence of "Napoleon" to achieve a dramatic conclusion. Gance's desire for innovative shots that required greater flexibility than traditional three-camera setups made it impractical to film the whole movie using this technique.