First, I'd only tag the episodes that have the content in them.
Second, NSFW or equivalent is just a genre tag and should not and probably does not have any greater effect on peoples viewing choices more than any other genre tag. As a result it should be treated as such. My argument is that in order for a story to be "complete" it must allow any and all content into it. That doesn't mean it needs to have it but it shouldn't exclude it because of some arbitrary childish nonsense which is exactly what the NSFW tag springs from. People can't on one hand be okay with violence and then on the other being like "oh but sex is wrong." Then go even further and say that because they don't like that genre, no one else is allowed to like it either.
It's literally like saying "Warning, this comic contains black people!" or "Warning, This comic contains a civilization who's technological development is less than or greater than current technological development!" or "Warning, The following program contains the word Apple!" For any of those it sounds ridiculous or even bigoted but for sex and swearing somehow it's okay.
It's censorship and supporting, allowing, or even tolerating censorship in any form is incredibly harmful to all industries and thus ourselves. People are perfectly capable of choosing what media they want to see for themselves. If we don't treat people like they're intelligent enough to take care of themselves guess what we're going to end up with? I've heard increasing numbers of stories on both sides where sometimes entire projects are shut down or held up because of really stupid emotional things and others where creators purposefully give in to the stupidity and put in what these morons want to see just to profit from their idiocy. The latter I don't really care about because if they're going to be that willfully stupid then they deserve to be exploited for it.
Genre tags themselves are very important. If I'm looking for something Fantasy or Legal Drama or whatever it's helpful when people tag their stuff as such. It helps me find them and them get exposure and a readerbase. Win Win. Especially since it's very common for stories to be multigenre these days. A lawyer having sex with someone happens in real life. Lawyers have sex drives too, who knew? If it has some kind of significance to the story because of character development or plot twists or something I don't see any reason why it should be left out because of fear of some bleeding heart who of course is oh so concerned about the children.
"But what if the children see it?"
Yeah, what if the children see it?
If somebody who's 25 or older never developed past the "eww cooties" stage that's not your problem. If they want to try hiding that by throwing toddlers at you because they don't want to admit that it's actually about themselves then they're pretty horrible people. They're the ones being irrational and stupid and they're the ones who need to grow up and live in reality. Do not shackle yourself on their account because once you start they'll never let you stop.
I personally like to say things like "Rated R for Reality. Warning: This media contains content that occurs in real life and is unsuitable for children ages 2 to 200. Viewer discretion is advised."
