The goal of the news or entertainment interview — any LEGITIMATE interview — is to provide to the listener (or viewer, or reader) an accurate slice of such factual information as the interviewee ("guest") is able to provide. In a best case, you hope he or she will also contribute a few colorful anecdotes, examples, or at least turns of phrase, which the audience may find entertaining.
You want to "bring out their voice."
Some subjects are a bit nervous — it can take a little work to get them relaxed enough to answer in anything but monosyllables. And of course some go to the opposite extreme: They bloviate, they filibuster — they may need to be nudged back onto the topic at hand, first gently, then a little more firmly.