Like no other Hollywood studio, Marvel uses a sophisticated version of previsualization (Previz/Previs for short) for its superhero films, which is far more detailed than classic storyboards. Thus, computer-generated moving images of what individual scenes in the finished film will look like exist at an early stage of production. For example, an early version in the form of a digital pre-visualization was produced back in 2016 for "Avengers Endgame" 2019, which has so far grossed a whopping .8 billion at a production cost of million and premiered in 2019. As can be nicely seen from the examples shown, the early pre-visualizations of "Endgame" by Marvel were often pretty accurately implemented in the final film.
The advantages of this approach are especially noticeable on such expensive productions that rely heavily on elaborate computer-generated VFX. Not only does it speed up the production process and thus save costs, but it also makes the entire film more predictable and exists in a presentable proto-version early on, which helps everyone involved in the film to improve individual shots. For example, directors who do not specialize in action films can concentrate entirely on the acting and plot, because, for example, the action scenes have already been planned in previz and only need to be implemented.
Scene from "Avengers Endgame" in the previz and final version.
Sometimes there are also different detailed versions of a scene, between which the director can then decide. Once it is clear how the pre-visualizations will be implemented, the next step is the "techvis" stage, in which, to speed up production, the Previs system outputs data on the scene in question, such as camera angles, movements and settings, so that the team on set can realize the desired shots exactly as planned, in some cases even using complex computer-controlled camera movements by robo-dollies or cranes.
And even after the actual filming, the pre-visualizations still help - so in the "post-vis" phase in post-production, the live shots are often combined with the parts of the pre-vis scenes (such as individual CG image objects like the background) to create a prototype version of the final film, which can then be shown to a test audience, for example, before the final film version is rendered with all the detailed effects and CG objects.