Just to clarify what I mean, I have seen some review articles that have bibliography items like this:
Bloggs, J., "The Paper that has Been Written", The Journal Title, Series Number, page number(s), (year). [DOI] [arXiv link]
where both [DOI] and [arXiv link] are hyperlinks to the paper, the former to its webpage on the journal website (with which it was published), the latter to its arXiv webpage.
Does the author cite twice just in case someone is reading it who might not have access to journals? Or is there another reason?