When you need to talk to someone
Eli Goldratt once said: Information is the answer to a question, everything else is data.1
If the question is known and unambiguous, then a web-page or automated phone service is often sufficient to provide the information required.
The problem occurs when the question is uncertain, or there is more than one answer.
In these circumstances one needs the assistance of an expert, either to refine the question, or to assist in choosing the most appropriate answer from a set of answers.