As with all things, it depends. Some general advice -- you should do this because it's a polite/courteous thing to do. As you embark on a medical career, there is the concept of "professionalism" which is a vitally important quality.
Most of the time, it does not matter. In large programs/medical school applications with rolling admissions, matters little to none. As prior responses have indicated, ratings/notes are submitted basically right after the interview is finished. That said, as you go higher and higher up in your training (med school -> residency -> fellowship) where there are fewer interviews/spots and something called "the match", which is the exact opposite of rolling admissions/multiple offers (lol). There are usually discussions at the end of the interview season to hash out the final order of a rank list of applicants to submit. Usually, the people involved in that discussion are the same people doing interviews. Is receiving a thank you note a checkbox? Of course not -- that's unprofessional and petty. However, does each engagement shed light on an applicant's interest, personality, other characteristics? Perhaps.
