I don't think they are useless. They keep the 'mystery' out of web servers. It is self limiting for folks when they see a piece of software and think of it as an impenetrable wall which cannot be breached or changed.
I proposed an internal web api at work for some hardware that needed to call out and test an address against a database of known problems. The initial response was the pain of setting up the infrastructure of a web server just for this one thing, was "huge" except it isn't really huge, its like 12 lines of perl or python code. People need to know that you can do that to see the pocket web server as a neat solution.
completely disagree. Want to create a quick file server to test a design or an html page in a browser? Yes you could use python SimpleHTTP but python is a dependency that not all times we have access too.