It allows you to write a WebSocket end point, in any programming language, without having to deal with building socket servers, dealing with WebSocket protocol handshake/parsing/formatting/etc, worrying about threading etc. Just write a script that reads and writes to stdin/out.
It appears to me that it is useful for eliminating the "middle man" scripts/code often written for web application and server interaction. If I want to create a web application that displays the status of my server (CPU, memory, I/O, etc) I can use this software to call vmstat directly instead of writing an API (PHP, Node.js, RoR, etc) that executes the same command or uses a library that requires even more code to get the exact same data.
I'm sure this this is probably because I don't have do this for work - but from that description it's hard for me to tell what the advantages are. A script to feed vmstat (or other command data) with a python socket would be ~50 lines or so.