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.
sees that you have quite mainstream fetishes, but if you want to find something more specific that wont work in any way. story codes do not include lots of possible fetishes.

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.
you seem to be quite intolerant if some snuff scene can ruin all story for you. cant you just skip it?
Of course if you write gay story and do not tag it properly you will miss most potential fans and attract lots of haters.
I still think that story codes are just for preliminary story evaluation to attract potential fans, so they must include only primary topics. If story has questionable content it is best to mention that in introduction or synopsis. Including just brief codes pollutes search results for those who wants exactly that stuff.

As I said torture is the same, what one might describe as heavy is another readers light.
I find that most of these "heavy" stories here are like bed time stories for kids.
It all depends on targeted audience sickness level. If you seek stories that involve spanking you may not tolerate breast skewering, and if you seek stories about body mutilation then obviously you will be able to handle spanking.
Story writer should take that in mind and do not mix large amounts of softcore with few lines of highly extreme content, because this will leave everybody unsatisfied, and story tags wont help.

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!
I failed to understand what you were trying to say here. What is "not so simple" here?