If a user posts a fiddle as their block of code, will this code be permanent enough in that we should allow that as the only code on the question? I am sure that this has happened a couple of times.
Are other similar sites permanent as well?
Those questions would be off topic. We cannot depend on external sites to make a question useful.
From the help topic on asking:(emphasis added)
To be on-topic the answer must be yes to all questions:
- Does my question contain code? (Please include the code in the question, not a link to it)
JSFiddle is useful for demoing and testing code, but links cannot make a question on topic. The question must be able to stand on its own.
However, permanence of the link is not the only consideration. A bigger issue is that Stack Exchange aims to build a Creative Commons-licensed body of knowledge, similar to Wikipedia. By submitting content to this site, you automatically contribute to the data dump.
Why is the data dump important? It's the community's insurance against Stack Exchange going dead or going rogue. Should Stack Exchange decide to put our good-faith contributions behind a paywall, for example, someone could theoretically clone the site based on the data dump.
I think that the General consensus is that,
if the Question doesn't make sense without the Fiddle then we should
(screenshots can supplement relevant code to show visually what the code does.)
so a Fiddle should be treated just like any other link (other than SE Site Links)
there is already a design in place that keeps someone from posting a JSFiddle link without code to go with it.
I think we need to be on alert about this issue though, to keep it consistent.