You can see the other person's reactions and detect nervousness or any type of lying and stuff like that. It's easier to get an honest answer as well, as the person is afraid that you'll see that he or she is lying.
You can see the persons reactions straight away. But normally one person has to travel to the other person. You dont have to wait for a reply like a mobile. Unless your talking to a deff person.
Advantages, as always are body language. Over a telephone or Internet you can not see the person and there is always the trust and suspicion aspect. If you are face to face you have broken down the...