This is a very old feature that (IIRC) all browsers copied that dates back to at least Microsoft Internet Explorer. I also recall people marketed it as a gimmick and came up with some silly names for it, e.g., "shortcuts". (I will try to find the originating browser and date it was introduced unless someone here beats me to it.)

Even today, Chrome presumptuously calls this macro expansion "site search".

I use it to access static pages. For example, I have local httpd's serving local pages on localhost addresses. One is a "clipboard" that I use in Chromebook "Guest" mode to output text from Chrome to a file descriptor, e.g., stdout or a file under /usr/local. This enables me to use UNIX utilities to process text from Chrome. (Chromebooks attempt to limit Chrome user access to the filesystem to a folder that the user can only access by using Chrome.)

For example, given the macro "https://127.0.0.8/%s.html", when I type "clip" in the address bar, the browser navigates to a local page

   https://127.0.0.8/clip.html

This page is an HTML form with a textarea where I can paste text that I want to output to a file descriptor, e.g., stdout or a file under /usr/local.

Another example is a static page that is a list of web search results from various search engines. These results pages are generated by a command line web search system I created using only standard UNIX utilities.

A final example is that I use "site search" to quickly navigate to chrome://settings pages with a single key, e.g., chrome://settings/clearBrowserData, chrome://settings/siteData, chrome://settings/content/all, or chrome://settings/searchEngines.

1. I find this label comical as I'm not a "developer". I'm just a computer user trying to work around problems caused by ad-supported "tech" companies in the comparitively rare instances I have to use one of their graphical web browsers.