For the uninitiated, generally NSFW is for sexual contents and NSFL is for gory contents. People may want to see one but not see the other at any time for any reason. I have seen this feature requested over the years in Reddit but it never happens. Maybe now some instance can finally implement it?
I can imagine they don't want accountants or IT people looking at porn while they work though. Their own websites are probably not filtered, but whether the work is for a porn site or a car manufacturer, you prefer them focussing on their work. For a content reviewer though, it's a different story.
That being said, there is not enough money in the world that would convince me to become a content reviewer. The shit they have to sit through is often utterly vile and traumatizing. Here is an article about a facebook moderator as an example: https://www.bbc.com/news/technology-57088382
I was mostly joking, but yeah, being a content reviewer has got to be a soul crushing job. I can't even imagine the shit you would see.