[Rinoa's actually quite capable of answering that question, and secretly a bit of a bookworm. So of course she's going to answer. Plus, ignoring him would be rude!]

Well, I'm not sure if it's quite the same here as it is back home, but.... usually they're for small things like bad luck, misfortune, evil thoughts, and that sort of thing. Probably a few for making sure your lover doesn't cheat, stuff like that.