Sure, some schools will check sign-in sheets for attendance at on or off-campus info sessions, but I don't see those having much if any impact on getting in or not. The biggest value of visiting prior to applying or interviewing is giving yourself some specific data points to use in your essays or when talking to your interviewer....or in the visit experience convincing you that you
don't really want to go to that school. You can use things you saw during your visit to talk about fit, specific things you liked, conversations you had with students in a particular club or career path, etc.
From what I could tell during my process last year, if you've already visited you don't really need to do an on-campus interview. Even if you haven't visited there's nothing that says you
have to do an on-campus interview...but again, you'll have a better opportunity to speak intelligently about the school if you've seen it in person, even if it was just for a few hours before your interview. Also keep in mind some schools (HBS in particular) may not give you the option of an off-campus interview unless you're deployed--you may have to come to campus for it.
As Spivey mentioned, ASWs are your chance to visit a school (or school
s, hopefully) that has admitted you and figure out which one you like best.