content-visibility enables the user agent to skip an element's rendering work, including layout and painting, until it is needed. Because rendering is skipped, if a large portion of your content is off-screen, leveraging the content-visibility property makes the initial user load much faster. It also allows for faster interactions with the on-screen content.

Assuming that an optimised 404 page is only required because users will mistype a URL in their browser is short-sighted. As the HTTP Archive data has shown, there are many other reasons why a user may encounter a 404 response (even if they have no idea they actually are!). The web performance impact of a users browser loading an unoptimised 404 page can be huge, and it can have a real impact on their experience of your whole site. All it takes is a forgotten file or misplaced ; in some JavaScript, and your users could be encountering it.