Shocker
As DarkArchon1980 said, tags are used to categorize your posts into the appropriate places to make it easier to both find or avoid content. I understand your point about spoilers - but it's nice for someone who has an aversion to, say....scat or piss (i.e. urinating on your victim in a story) to have a heads up that they may want to pass on reading a story.
Likewise, a member who likes to read celebrity non-con can easily find content by clicking on the "celebrity" tag.
I've seen numerous examples of a reader noping out of a story or being pulled out of the fantasy world you've created due to the sudden introduction of elements they aren't a fan of. Not a perfect system, agreed but our authors are so creative ( ❤️ you all) there are usually surprises, twists and turns regardless 😀