This would be great for a locally-developed website, especially for developers who can't afford or don't want to host their site elsewhere!
I have a collection of HTML files on my tablet's storage that I access regularly without turning on wifi since it saves battery, I don't always have wifi, and my tablet is slow. It is a hack, and only Firefox does it, which I am thankful for. And it only works on old Android versions (9 maybe.? Lol). You have to hook up your device to a PC running Firefox and then remote debug your device and set the URL from your PC to the correct file. And never close that tab after that!
I guess another workaround is to run a local HTTP server.