I saw a person upset because she was being targeted with nasty comments from other people in other random subreddits about her concerning her mental health.
Some of us like to keep certain details of our lives private from other subreddits such as this one we are in now. Some may not care. It was suggested to her to make 2 accounts, but here is another way.
You can hide comments and details by going to “You” (your profile)-> “Active in”-> “Content and Activity”-> “Customize”. Now you can select and hide any community, post and comments from public viewing.
Hope this helps. :)
Edit- I want to add that you can turn off “show up in search engine results” in settings.
This is not “private”… but away to hide select communities from your front page.