I disagree, I think this site's advanced search is very powerful and can find (taking it stories are well coded) exactly what you are looking for. Google on the other hand will just find instances of your search, data mining at it's worst.
Again I have the other opinion, story codes for me have two purposes, one to find what I'm looking for, I can often glance over a story's codes and decide if I will like it or not, two is to find stories to avoid. One man's fetish is another man's poison for instance personally snuff is a big turn off and I definitely want to be warned about it.
Another, I remember in college browsing alt.sex.stories and reading a Star Trek story only to find out the hard way it was a gay slash story - I can still (against my will no less) recall the scene!
So for me story codes are vital, now the subject of when you should use a code is interesting. It's not that simple as you mentioned, if you list scat but only have a light scene, the scat fan would have been disappointed and the non scat fan could possibly miss out on a good story. Even more confusing some fetishes encompass several aspects, take for instance Scat (Torture is another example), I read the wiki entry some time ago and remember thinking Coprophagia , omg that is disgusting! Do people actually find that arousing? (Hey everyone to their own) but at the same time I find enema and forced expulsion as part of slave training/sexual discipline very arousing, both scat very different ideas! As I said torture is the same, what one might describe as heavy is another readers light.
I think you need a good synopsis and chapter introductions, if you mention a story code in a chapter that is well questionable, then explain briefly why it is there to help the reader.