Until they have a filter in place for people to choose from the only things I think should be flagged are blatant plagiarism of other steemit posts. If I work hard and make a great post, and you take my post, copy and paste it and post it as your own.
Or obvious first IMAGES as graphic porn, or violence without a warning and allowing the person to OPT in.
If they setup a filter of some sort so you could opt in to seeing those images permanently then I believe no warning would be necessary NSFW or something like that.
At the moment it is beta and no such thing is there.
There are a lot of down vote brigades happening, and hate, and anger on things I believe people are missing.
I just wrote that... at the bottom I link to an article I wrote this weekend about down vote brigades that I think ties into and is relevant to censorship.