Disclosure is a kind of ritual -- meaning, it's a social act that can change your social categorization. Kind of like marriage. If you don't pass, or you're just starting out, it's a way to change the gendering people give you -- in general, you'll be gendered "trans" instead of what you were before. Which is wonderful! And sometimes very gracious people will skip the "trans" gendering and gender you properly.
If you're already being gendered correctly, the ritual of disclosure can have quite similar consequences. In general, that proper gendering becomes modified towards a "trans" gendering.
I've been properly gendered for close to two decades now, so I don't disclose (with a couple of distinct exceptions). I don't tell colleagues, or acquaintances, or people at the grocery store. I don't tell my very close friends. I don't tell lovers. And no one asks.
There are two exceptions. First, certain kinds of medical care -- namely, maintaining my hormone regimen. This doesn't include things like dermatological treatment, electrolysis, hair transplants, broken bones, what have you. The second has to do with relationships with other transitioners -- like this board, for example, and any subsequent friendships that develop through trans environments.
This gives me such peace of mind. In my experience, there's nothing more healing for dysphoria than proper gendering. I kind of believe that disclosure is a contraindication, medically speaking, at least for me.