At what level are mature content tags necessary?
Apologies in advance for the out of the blue question. I want to make sure things are properly tagged before putting them up so people don't go in with false expectations.
For traumatizing, I would generally put that on if you have content that's related to any of the common things you see on the more concise trigger warning lists, if that helps at all. Also, I would personally put it on if you have violence, abuse, or death happening to children or animals but that might just be me.
I am pretty sure 'stranger in a strange land' didn't require a friggin red skull and crossbones even though it had sex, cannibalism, and people who's moral values closely resemble barnyard animals as the heroes of the story.
If you think there's something in your story that will make the legion of professional haters clutch their pearls, throw a content warning in there so you can rightly claim they were warned.