It's true that the test only tells whether or not you have antibodies, and does not tell anything about the location of the infection. To figure that out, one must use other information.
Almost all hsv2 infections are genital, so if the test is positive for hsv2, you can be pretty certain that it's a genital infection. Most people who don't get outbreaks will get minor symptoms that they can be taught to recognize. Knowing that you have it gives you the ability to take precautions against transmitting it, and thereby reduce the chance of transmission.
Just because you have no symptoms does not mean that your partner will have no symptoms when they get it from you, and those who contract it with the foreknowledge that it was a risk tend to deal with it better than those who got it as a surprise.
Almost all oral herpes infections are hsv1, but not all hsv1 infections are oral. Genital hsv1 is fairly common in the general population, and it's very common in certain populations. Young people are more likely to get genital hsv1 than older people are. Older people are more likely to have already acquired oral hsv1, which pretty much prevents a subsequent genital hsv1 infection. There might be differences in how older vs. younger people use oral sex, but I'm not going to guess at any statistics on that.
People with only hsv2 appear to be less likely to acquire hsv1. That may be an understatement. I think there are only a few documented cases of it happening.