V much depends on your profession, but when this happens at my place of work, they have usually already decided but either their manager wants to meet the person as well or they just want to run it past other people to be sure. Sometimes 2 candidates can be v similar in terms of experience/what they bring; then it comes down to personality.
It's usually a lot more of the same. Think back to your first interview, anything you would have preferred to go/say differently. Have you been asked to prepare a presentation or anything?