When my relationship went poly (I'm the "hinge" of a MFM "V") we decided that we would each choose how "out" we wanted to be about it, based on our own personal comfort zones. I couldn't force my other significant other into a closet, but I couldn't drag him out of one against his will, either.
However, we had a bad experience early on that left all three of us very wary about who we felt safe being out to and more than happy to stay in the comfort of the closet.
What happened was that I felt okay telling one of my oldest friends that my platonic male friendship she knew about had developed into a romantic and sexual one, and it was all above board and my husband was not only accepting but happy about it. Unbeknownst to me, she was emotionally unstable, and had some very serious fidelity issues going on in her own marriage and my revelation triggered her into a full-blown freakout. She went into rage and attack mode and made threats to out us to our families, employers, friends, community, etc... if I did not break it off immediately. She claimed to be doing this for my own good, taking drastic measures to "save my marriage". I told her I could handle my love life without her help and my O.S.O wasn't going anywhere. So she decided he must somehow have had me brainwashed, and decided to target him as an outlet for her rage. She started stalking him online, made up fake profiles on social media sites to gain access to people he knew, and contacted a few women to "inform and warn" them that he was cheating with a married woman and trying to destroy her marriage. She posted what little personal information she knew about him on some "cheaters" website. And sent emails to me trashing him. Lots of frothing, raging, psychotic, hate filled emails. What got to us wasn't just her threatening (and actually) outing us without consent while justifying it as concern, but the level of anger and hatred she had going on while she did it.
The three of us are all really laid back, peaceful (and conflict avoidant) people who just want to live our lives without hassle. The thought that *one* person could wreak so much havoc in our lives and potentially cost us jobs, homes, friends, etc... made all three of us decide together that it was more important to be safe than to be out. But, over the years, we've come out to select people as we feel comfortable doing so. Various family members, friends, and coworkers know and are fine with it. A couple others weren't and decided to no longer be friends with us because of it, but that's their right. The neighbors know something is up, but not exactly what, and we really don't care what they assume.
So, we're out to who we each feel okay being out to, and that's what works for us.