I've actually only had good experiences and thus advantages with disclosing.
But I believe, from reading and participating here, that sadly, that's dependent on the caliber of the people and the nature of your relationships.
Lets start with my mom and siblings (my dad had passed on by the time I was dxd)...
My siblings were immediately supportive and my mom went into denial until she read a few journal entries... I didn't blame her though, she's of the older stock where MI isn't or wasn't an actual thing.
But she's come around, a lonnng way around since then.
The advantage? They are more empathetic during my depressions, and understand that I don't necessarily have a "reason" to be suicidal.
Also, nobody bats an eye when I do washing at 2am or scrub the tiles till sunrise.
My mom and brother even chip in and help take care of my daughter when I'm barely functional. No judgment.
My daughter, she was 6 when I told her, because she was worried about mommy's crying and anger and wanted to know if the doctors could help and how.
That was 6 years ago, she understand my mood states are not a reflection of her and doesn't feel frightened or disconcerted by them anymore.
Bf / friends, advantage is I don't have to make up half truths about why I am behaving a certain way or why I keep bailing on plans, they show me nothing but compassion.
Work, I've had incredibly supportive coworkers and more importantly managers, who schedule me around my therapy and pdoc appointments, give me low stress tasks when I'm struggling and don't treat me differently when I need time off or went inpatient....
With the exception of work, my disclosure was a light bulb moment for everyone else. It was like "Aha! That explains alot!" Because I didn't go all bipolar overnight, my BP developed in my early teens but was only dxd in mid 20s.
Anyway, I'm thankful I've gotten a warm reception from every Tom, Rick and Harry that I've told, I know I am very blessed in that regard
Also, I would like to add that it's very librating to not feel like I have a dirty little secret...