This is not unusual at all, many companies have this feature. It means there is a live customer service representative to answer your questions right away. As you say email is ok but you have to wait for an answer and emails occasionally end up in cyberspace never to be answered. Personally (as a customer service rep) I find email a PITA, replying back and forth, much easier to pick up a phone or use the live chat feature.
Remember the chat feature is only available during their business hours.