If you're thinking of tags as keywords, my understanding is that they are only keywords inside of HP. I use no more than 10 tags, but I think you're allowed more than that. When you tag, it provides more related hubs to be shown on the right side of your screen. So it can send your readers to other hubs.
However, if you look at which links you've received traffic from, and some are from inside HP, that means you're also getting links from inside HP via your tags making yours a related hub displayed on other hubs.
If you're wanting to use keywords, I learned more about how they are used in HP by reading some hubs by rtrapp and Peter Hoggan.