Giving the patient some control over the interview tends to put them at ease. If you'll notice the arrangement of most exam rooms, you'll find that more often than not the patients chair is next to the door. If the modesty of the patient is respected when partially or completely disrobed you will find greater ease in obtaining the history. When patients are uncovered they are often so self conscious they have difficulty concentrating on your questions or their answers. Both interviewer and patient communicate in more ways than the spoken word.
Nonverbal communication is very important during the interview process.
A frown or a raised eyebrow by the interviewer may tell the patient of your disapproval. The patient will become very cautious at this, and may withhold information to avoid being scorned again. The tone of voice used and the appearance of the interviewer are equally important.