When a user has multiple questions closed, the system sometimes notifies moderators, who might contact the user. There is a template for mod messages that covers this case, so it seems we're supposed to (sometimes) send such messages.
A good duplicate helps the site, but a lazy duplicate, or one that is worded essentially the same as the original, is something we want to discourage. Fortunately, the system suggests possible duplicates as you're asking, so the user can avoid asking a clear dupe -- if he's using the full site.
Someone asking a question using the full desktop version of the website is shown a list of potential duplicates as they ask:
However, someone asking same question using the mobile version of the website is not shown possible duplicates.
Therefore, what platform a user asked a duplicate question on affects what a moderator should tell them, in case the moderator needs to contact them. If they used the desktop site and still repeatedly ask a poor duplicate, we want to point out that they should cut it out and how they can find previously asked questions before asking. If they used their phone, we'd need to tailor that information to someone who doesn't have the list appear when he asks. Knowing which platform was used also may affect, in some cases, how much good faith the moderator should ascribe to the asker.
It would be helpful, therefore, for moderators to be able to see what platform each closed-as-duplicate question was asked on. Ideally, this would appear in the multiple-closed-questions list, and perhaps also accessible from each question.