Imagine if you owned a subway shop, and someone came in with their own meat, and asked you to use their meat instead of yours on the sandwich. How would you feel about that?
Posts that rely on an outside link for their primary source of content are generally not allowed on any SE site. In answers, we require that the answer itself contain the answer to the question, with a link to an external site as backup, not the principal source of information. Same with questions; we expect the question itself to be the primary source of information, not an offsite link. This includes links to websites as well as resources like jsfiddle.
There are many reasons for this, but the primary reason is that all such links are temporary. When the link goes down (or the content at that link changes), it renders the question useless to others.
If you can't convey your message with pasted code that fits into a post, perhaps your code is too long. You can't really expect answerers to pore through pages of code in an offsite link and expect to receive comprehensive analysis in a Stack Overflow answer. See http://sscce.org/ for more about this.
Keep in mind that links to jsfiddle are not expressly forbidden, but you are expected to include a code sample with your question, in addition to the fiddle.