This tag (and it's new form just-for-fun) have no purpose on this site and should be eradicated at our earliest opportunity. It's a meta tag and those should be removed with abandon. It was created to justify a question that does not fit our guidelines. If we'd like to allow that question, let's just allow that question and not invent a meta tag to make it somekind of sacred cow. Creating a new tag for it was probably the worst possible idea when a comment below the question indicating that it was discussed on meta and approved would have been plenty.
Here's the fundamental problem with having a tag for this:
- It encourages more questions just like it.
Questions that would merit a "just for fun" tag (other than the one that it's been applied to, as it's a bit of a different category), are what we'd call GTKY (Get To Know You) questions. These questions are terrible fits for SE as they break the voting. An occasional one can be good especially if it attracts experts, and would be acceptable on meta. However, the main site should not be the place for them. More importantly though, the very existence of the tag encourages more of this stripe of questions and is a broken window. We don't want more of these, if we allow a few tightly controlled ones, that's OK provided there is consensus, but having a tag is basically saying "ask whatever GTKY question you can think of" and then we're down the slippery slope of "What's your favorite class" and "Monks!"