Human speech contains a greater concentration of behavioural markers than any other channel (IM, Web Chat etc). Human speech contains linguistic markers that do not typically manifest when typing something out instead. Human speech also contains vocalic markers such as pace and cadence that by definition are not available through other channels.
You already ask the questions of your data that you know to ask. But what questions do you not know to ask? An actionable insight doesn’t merely answer the same old question, it drives action and makes you rethink which questions you should be asking in the future.