Imagine having clinics inside your settlements and having sick or injured settlers come in from time to time for an appointment.

If you have stimpacks you can help them to recover or things that treat radiation poisoning or other medical emergencies and get praised by the people you helped and gain karma.

Doctor is the same as a barber.

I imagine that having a clinic has similar or slightly greater requirements that having a store is... ie the appropriate charisma perk at a given level.