When my son declined some offers he received very polite emails in return making me think it is much appreciated when you let them know.
Obviously if you or your school does not have a relationship with the Regional Rep it is not necessary beyond letting them know to check the box declining, earlier if possible.
For certain schools that my school has a close relationship with, does it help if I decline, if I know there are people from my school for whom a decision has not been made? Just curious
With regard to what I said before I was talking about situations where someone advocated for you or at least answered your questions or responded to your emails of interest because they are your regional rep or the assigned contact for your school. That is the same person your GC will be talking to when it is time for your brother or sister or someone from the Class of 2020 to apply. On more than one occassion before decisions were made I was asked by my school how do I feel about X College because I know the GC talks to the Regional Rep, that is their job (it is not just to fill out the evaluation form).
My rule of thumb: If an admissions rep would recognize you if you were back on their campus (D has 3 of those), send a written note.
If the admissions rep has a relationship with your high school, send a polite email.
Otherwise, push the decline button.
My D hit the decline button for her schools that had one (after she submitted her deposit for “the one”). She just received an e-mail from the Director of Admissions asking her to get in touch if she’s not happy where she will attend. Nice!