At what level are mature content tags necessary?

#1
Heyo, I like writing horror stuff, and while I do enjoy darker and more mature themes, I was curious what the 'line' was that would require a mature content tag. I know I'm using gore and profanity tags already, but do fade-to-black romance scenes (rather than explicitly showing) and sexual jokes necessitate a mature content tag on its own? At what level does something count as traumatizing? 

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.

Re: At what level are mature content tags necessary?

#2
Fade to black doesn't need sexual content tag imo, but depending how involved the sexual jokes are, it could warrant the tag. If it's rare, then just figure it's included around profanity. Otherwise, for frequent sexual jokes, I think it warrants the tag--at least I did that for my own story. (One participant in the main romantic pairing can feel soulmate bonds, just straight up tells his soulmate this, so then they're hella awkward around each other in the beginning and make lots of sexual jokes. That's what I did that I thought warranted the tag, anyway.)

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.

Re: At what level are mature content tags necessary?

#3
Mostly the content tags exist so that people with an axe to grind will leave you alone.
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.