I don't know the details of which benefits VN offers to Skyteam partner elites, and the below might not apply to all airports, but speaking generally the things that come to mind for me would be

- maybe access to preferred seats?
- expedited security lane? you could probably get around this by showing a separate membership card but that's one more thing to juggle, and if they insist on it being reflected in the BP then it potentially saves a trip to the checkin counter
- speaking of, maybe access to the priority checkin lane
- peace of mind in the sense of having it taken care of in advance and one less thing to think about or potentially forget

I'm curious though if there is some particular _dis_advantage to doing it in advance? Other than the time/effort involved I mean, which of course everyone will weigh differently depending on how important these sorts of things are to them personally.