I've heard from most medicine PDs that a second look does not help us move up the rank list at all, it is only for the applicant....it might be helpful to you to figure out how much you like a program if you are still unsure after the interview day.....However, this might be variable from program to program. People I know applying for surgery have been told that it will "reflect positively" on them to come back for a second look.
Basically, all it entails is coming back to the hospital, meeting up with the PD and/or chairman and hanging out with one of the chief residents for part of the day, going to attending rounds and whatever conferences they have that day.
