Placebos are used every time you take a real medication, paradoxically. A researcher might try to discover the effect of the drug alone, discounting any benefit which is due to the placebo effect. However since both work to treat the patient, they are both of use to the clinician.
If we ignore ethics, it seems then that clinicians should constantly talk up the value of any treatment plan. They should do their best to both treat, and convince the patient that the treatment is going to be effective. That way the clinician gets the most out of the placebo effect and the treatment.
The real challenge comes from the ethics. How do you have informed consent, if your doctor is constantly talking up the treatment picked out.