I think it's really useful to tag things in a story to make it easier for people looking for that kind of thing to find it, and I love that AO3 enables this in a really big way with its tagging system, but this also often conflicts with my desire for certain elements of my stories to be a surprise.  And of course my stories aren't going to be spoiled completely by the tags regardless, but it's just like--it's generally considered a good idea to list major pairings, characters, tropes, and indeed I really, really like to list these things, but listing them also sometimes conflicts with creating more of an opportunity for certain aspects of a story to be a surprise.  So it's really hard for me to choose between them sometimes haha.