The benefit of the in-person interview is, more or less, just for you to determine if the area, the school, and the students are right for you. It's certainly possible (probable?) that there may be some unconscious bias (both positive or negative) with an in-person interview versus an online interview dependent on how you present yourself, but I can damn near guarantee you that there isn't a box on the committee's sheet for you that says you gain or lose favor one way or the other.
Personally, I think it is easier to present myself in a positive light in a online interview as you don't need to worry about body language or half of your interview attire. There's no risk of accidentally getting mustard on your white shirt during lunch and not being able to change, and nothing beats the comfort of your own home.