The DPR is important because of the above reasons.
Patients come to see doctors for help with problems they believe require medical interventions.
These are rarely pure biological problems. The underlying disease, if any, almost always has an overlay of illness that also needs attending to. Even when someone presents with a simple sore throat, there may be some occupational or family reason why they have come at that time. This way, instead of just treating a sore throat you might prevent a suicide. Even if the patient is not depressed, they would probably appreciate your question as an expression of your interest in them as a person, and at very least leave with a much more positive opinion of you.