Adding "Sharktooth" as a tag doesn't help people find the Sharktooth Necklace. One can easily find the Sharktooth Necklace by entering "Sharktooth" into the search box on the upper right, even without its getting its own tag.
There is also no particular utility in tagging all the necklaces in-game, though I will grant that if somebody were to tag all of them, it might have some value as trivia.
Tags are useful for categorization, for finding other members of a set. Tagging all eight Lost Weapons (and no other items) "lost-weapon" can be of use for those trying to get them all. On the other hand, adding "Jet" and "Set" as separate tags for Soundless Jade, as you have just done, certainly doesn't help anybody find that item. Tagging Book of the Twillight "lost-weapon," as you did the other day, is outright misleading, as it's nothing of the sort; as seen in the text for the Cursed Wave trophy, there are only eight of those. All superfluous tags do is add clutter and make the tag system less useful, making it harder to find the signal amongst the noise.