I love it when I hear someone use this phrase. It tells me that they are interested in the person they are talking to, and it encourages them to explain themselves more fully. I just heard this used in an interview when the subject of the interview said something provocative. I could almost hear the change of gears as the interviewer pivoted from what they were going to say originally to saying, “Tell me more.” What followed was a fascinating insight into the interviewee’s viewpoint. I certainly learned more than if a normal rejoinder was used.