[pgbovine]

creator of http://pythontutor.com/ here ... skulpt is great and i know one of its maintainers quite well. one use case that's important is using it to distribute self-contained zero-install tutorials onto computers such as school machines and those in less-well-resourced parts of the world without good Internet access. you can deliver an HTML/CSS/JS zip file on a USB stick or CD-ROM and get lessons up and running even without Internet access.

that said, though, one reason I haven't made the plunge to Skulpt and still choose to run Python server-side is that as students get more advanced, they will inevitably run into edge cases and other weird behavior where skulpt will not match CPython, and the error messages and other outputs they get will become inconsistent with expectations. that's why i still continue to run CPython server-side in a sandbox for http://pythontutor.com/