What are the downsides of using arXiv references instead of conference/journal references for the same paper? I read in the instructions for one conference:


  Please do not use arXiv references for papers that have been published at official venues such as conferences, journals or workshops. Please make the effort to identify these at least for all papers prior to 2017.


What are the downsides of using arXiv references instead of conference/journal references?
Using arXiv instead of a conference / journal reference has an obvious disadvantage: readers won't know that the paper eventually passed peer review and was published.  This is important context, especially if they want to cite the paper themselves later.

Using arXiv in addition to a conference / journal reference might make sense, but some might consider it redundant.