/favicon.ico fetching by everything is still a thing. For server administrators who want to conserve bandwidth for more important things, they need to made the server response as short as possible. If sending a “204 No Content” HTTP Status code isn't possible, then the goal is to send the smallest valid ico file (which is 70 bytes). Modern web browsers usually scale the image down to size so hopefully a 1x1 pixel image will scale up to a solid square of color. While you're at it, put something at
/robots.txt as well.