Doctor's notes are of pretty limited value now with limitations on medical inquiry.
Doctors are oath bound to act in their patients' best interests. If they think their patient could use a few days off for a mental health break, they'll write a note. If their patient has a bonse sticking out of their skin, they'll write a note. The problem is that you can't really tell which underlying issue gave rise to the note because the note simply says that the EE is under the doctor's care and has been since date X and will continue in that capacity until date Y.
I'm not saying you should or should not get doctor's notes. They can play a variety of roles in managing leaves and attendance but I argue that their role in workforce management is vastly reduced with the advent of privacy and limited scope of inquiry.