Heh.  This was really bugging me.  I remembered it clearly, but I couldn't find an issue.  Thought maybe it was a comment in the code, but nope.  Google led me to this line in the docs: "It is no longer necessary to use the global tempdir variable."  Checking when that was last changed, it turns out it was by me in issue 10354, which is the issue containing the discussion that I was remembering, but that was about template.  

Nevertheless, I think the sentence in the docs itself could be considered a documentation deprecation.

Since you are arguing that it shouldn't be considered deprecated, I think we should get some more participants in the discussion.  I'm +.5 on explicitly documenting it as deprecated.  I'm adding a couple folks from issue 10354 who might have an opinion.

Note that if we do keep it in the main section, that sentence should still be deleted, since it looks like "it is no longer necessary" has been true now for longer than it *was* necessary.