Have you ever executed a script you didn't write? It's handy to have a runtime where you can see what a script can do from its permissions.

I'd generally like to see more languages with APIs for untrusted sections. If I know my program reads e.g. paths from untrusted files but should only ever access it's own folder, it would be nice to have a way to ensure that I can't get tricked into accessing something outside of it.