Nope but it is some form of metric that you can use to judge the doctor's capability.
With a self-taught doctor, you just have the questions that you ask to help you judge. With a doctor who's been through school, you have both your questions and the fact that he/she has been through what has been set out by the school issuing the degree.
The degree is for his/her own benefit. What I care about is whether the doctor is smart and well-informed.
No, I don't think that earning the right to use the suffix "M.D." means that the doctor is well-informed and knowledgeable.