It honestly depends on the situation an individual is in and how they want to live their life.
For example, someone living in Russia I could not, in good faith, suggest to come out to anybody except perhaps very carefully chosen friends and/or family members and/or romantical partners. Coming out to any and everyone would be a foolhardy, dangerous venture that would net nothing but perhaps a martyr. Depending on how you view it, the best case scenario is either death or "prison".
Someone living in, say, Ontario, however, I'd say come out if you're comfortable with it. I advise coming out to romantic/sexual interests as soon as possible, A) so you don't get attached to someone who is going to dump you over an aspect of your life and body over which you have little to no control and B) so you can be honest with said person. Someone living stealth may want to wait longer than I, who is quite out. With, like, everyone.
Personally, I'm very out. All my co workers know (almost) all my family knows. All of my friends know. It's in profiles I have online.
I view where I came from as an important part of my history, and having trans voices anywhere is important. Visibility means more education means more acceptance.
But I totally understand people who want to live stealth. 100%. I thought I'd want to be that way for a long time before I realized that I'd do more good as an educator. That kind of role isn't for everyone. It's not a bravery issue by any means. It's a "threshold for BS" issue, like any educator has to deal with.
People have to choose what's right for them. With the exception of people you are going to be/are in a romantic, sexual relationship with, I don't think there's ANYONE you have to tell. On a personal level, I think trans people should tell people that they're intimate with about their history. I feel like keeping something like that from someone you're in a relationship with is a huge breach of trust.
I read an FML once where the OP got literally to her marriage bed with her new husband and found out right before they were about to have sex for the first time that he was a trans dude and hadn't had a phallo. And people were raging at her for being "transphobic". That's not transphobia, IMO. That's someone who you trusted keeping an enormous secret from you, essentially lying by omission. To me, that's unacceptable. Again, just my opinion. YMMV.
But with the exception of that, I don't think there is anyone any trans person absolutely HAS to tell. Not everyone has to be a crusader for trans awareness. I think most people would rather just be able to live a quiet, average life as average people (I know there's a better way to phrase it, but it's not coming right now. Many apologies).
If you want it something only select people know, that's your decision. No one should take it from you. And in any case, no one should out you without your permission.