Because reports are a part of every operation, records must be kept in the field as well.  As a part of being in the community, police are held accountable for where they are, what is happening, what they are doing, or recounting what happened that the officer arrested someone.  Cameras in the squad cars now help with reports, but essentially, the officer is responsible for  making accurate, timely reports.  As a volunteer crisis counselor in a county jail, I have watched many officers bring in a prisoner, and then stand there filling out the rest of the paperwork.  The public record needs to be kept accurately, and the lawyers and judges depend on good records being kept.