At my school, current grad students fill out review forms regarding our interactions with prospectives. Obviously faculty make their own decisions, but they do tend to consider our impressions. We had a case recently where most of the students expressed concern over a particular applicant, concerns that were largely ignored. At least one faculty member has since expressed that they wish they had listened more to our hunches.
The take away is that you should realize that you are being appraised with every interaction, the moment you arrive, from the current students, the departmental secretary, and the faculty. Just be your charming self, and be polite. Treat people how you would like to be treated.