The advising office at NU doesn't write recommendations for you. They collect recommendations from Northwestern faculty and staff and will put the letters together and send them to schools for you. It is quite convient and much easier than asking the recommenders to send the letters for you.
I didn't use the office that much as Dean Weimer used to be the adviser and not to be blunt, but he really sucked. The new person is supposed to be much better, but I have no experience with him (I think it is a guy).