Health care providers need to keep records of treatments offered to specific patients in order to determine the effect of those treatments upon medical conditions and to assist in modifying treatment plans as indicated. If there was no record of medication prescribed and its results or of therapies ordered, there would be no basis for evaluating effectiveness for that particular patient's condition.
Patients need to keep records of what treatments they have received so they can be aware of what has been tried, how they reacted (the patient knows best how different medicines or activities may impact the way s/he feels!), and what difference may have been felt through modifications of dose or therapy.
There are an infinite number of variables that impact treatments for medical conditions - the only way to attempt to identify which factors have significant impacts upon any plan of treatment starts with meticulous record keeping of all those variables.