It's very exciting when industry unrelated tools and work can be used for other purposes. In this case, web sites and animated movies. It seemingly doesn't really go together. We're used to seeing animated vector graphics and they can definitely be great, while animated banners are made out of a number of images, clever timings and movement. 3D animations are a different sort altogether.
3D rendered animations are not too dissimilar to 2D animated banners in function, and can also feature written text instead of it being part of an animation (though it can be), adding to your indexable content. This however, is where the similarity ends. In 3D, what we see is environments, models, physics, lighting, cameras and more, which give us nearly unlimited possibilities meaning there is practically no limit to your vision. We can use, or create effects, particles, shaders in all sense like making a movie or a game. And it can be as realistic, or as stylized as you like.
On this website, you will find the footer to be a good example, it serves as a background for standard content. It's a short 5 seconds clip made, rendered and recorded in Unity. 'Weighing' in at only 3.5MB, its light footprint means it doesn't have a negative impact on loading times, and will keep the search engines happy.
Since these animations require a lot of time, reiteration and building block to make, they aren't exactly cheap. We reduce these costs as much as possible by mostly using readily available assets and tools, in particular 3D models. Where needed assets are not available, we will either do the modelling, or reach out to one of our partners, depending on complexity. We will not however accept a project that is beyond our scope or ability.