Good Subjective, Bad Subjective refers to the Back It Up principle that was developed on an early SE site. I've seen this principle in use on UX (though I can't find an example right now), and citing sources or experience is standard on Mi Yodeya.
Backing up an answer includes citing sources, making a logical argument, and sharing relevant personal experience. The idea is to show your work rather than to simply assert something as true.
How widespread is the Back It Up principle on other sites where "compile it and see if it works" doesn't apply? Can answerers, err, please back up answers with links to these policies where they exist?
Edit: While I appreciate (and have upvoted) the answers received so far, I am still hoping for a comprehensive list. I understand from the answers and comments that Gaming, Skeptics, SF, and Workplace have forms this policy; who else, and what shape does it take for each? Ideally one answer would list and link as many of them as possible.