I was wondering because I want to apply to alot of colleges around the nation and I don't want to spend money on travel when they are not even contemplating accepting me.
No, most colleges factor in your interview in the admissions decision, and then they send you an acceptance or rejection letter. Although there are many schools that do not require an interview, or it is at least optional, so you won't neccisarily be traveling around to every school you apply to unless you want to interview or want to see the campus.
Yup. Interview is just bonus points, and small ones at that.
But if the college has an alumni network, sometimes you can be interviewed by an alum in your area and they'll submit their rating of you to the college, and that can count for something.
If you have no chance and they don't like you, why would they waste their time setting up an interview and sending someone to interview you? Thats my thought but thats more of graduate (vet) school. None of my schools do interviewsd so I'm not exactly sure how it goes, but thats my guess.