As a patient, I want to know that the person working in my mouth has had a certain level of training.  I can usually tell when an assistant has been formally educated or not.  I've been to dentists where the dentist did everything and the assistant basically handed him things. And I've been to dentists where not only did the assistant do most of the work, she was so knowledgeable, and explained things to me so completely, that honestly, I thought she was at least a dental student intern if not the doctor, until the doctor came in the room and I saw that my assumptions were incorrect.  The assistants that can explain things to me, tell me what they are doing step by step and why, they make me more comfortable in the chair, that I am otherwise a little nervous to sit in.  If I have to worry whether the assistant who is placing my filling was trained in an accredited school or was taught on the whim by a doctor, maybe not even a doctor I know or trust, then that is going to hurt my confidence and trust in the profession, a profession that sometimes gets a bad name anyway.