I don't use ed interactively but find it's really useful in shell scripts that need to edit files - heredocs or piping printf output (like one example in the article; never felt a need for something like his xed). Even used it in a C program via popen() to edit settings in a config file.

ed is underrated.

(I'm responsible for suggesting GNU ed accept posix EREs; think I got the idea from NetBSD's version)