It’s cheaper, but you already knew that.
If it comes to a choice between two applicants with almost identical qualifications and ECs, I think being an in-state applicant will help you. Some schools have a limit on how many OOS students they accept, simply because they are, at the end of the day, aiming to serve mostly students in their state/area.
Interestingly enough, though, [this article](College Admissions: Which State Schools Give an Edge to Out-of-State Students) says that more state schools are accepting OOS applicants.