To be honest I forget about the NSFW tag half the time and put it on the other half even though I feel that it is somehow a prostration to the puritan movement of the modern internet.
The thing with Steemit is that it is rather unruled, but people can flag you for whatever reason they like. I think that a warning in the first line (so people can see it in the preview) can be a good way to warn people without using an actual NSFW tag, but as you can see no one has complained here even though I forgot about it.