I think 'vital' is quite a strong word to describe people's wishes to be able to put their relationship info on fb like mono people can. I can say for myself that it definitely isn't vital, it's just the unfairness of it that bugs me. It really depends on a person's way of using Facebook overall. Some people share more than others. If you'd be the type of person who would put a relationship status on fb if you were mono, that probably doesn't change if you're openly poly.
Me: bi female in my 30's
Live-in partners: Hank and rory
Partners: Yvonne and Ash