This has nothing to do with servers though. It's in context to the requested resource. If you want to check if a server is alive it's happening several layers below an HTTP request.
Right, but, the word "server" is often used to refer not to the physical machine, or even a virtual machine, but to the "web-server" meaning a running instance of Apache nginx or IIS. etc.
Not saying such a feature is needed just wondering could it be useful for some purpose.
Not saying such a feature is needed just wondering could it be useful for some purpose.