will think of an answer, and you avoid the awkward silence. you not only kept the conversation going, but you also know what the conversation will be about since you choose the topic.
you should be able to follow the conversation a bit better since you know what they will be talking about.
after they give you their advice, you can politely end the conversation there. of course, if you feel like you are keeping up with most of the conversation, or are clicking well with that person, feel free to continue.
however, if that person is speaking too fast or not clearly and you are having trouble understanding anything, just say thanks, 