My understanding (could be wrong)
I believe they have different specialists / specialties, and therefore can prescribe for more / fewer / only certain conditions accordingly
Depends which type of Dr's each clinic has (which ones they want to hire) I think. E.g. need a consultant psychiatrist if they want to prescribe for
ADHD / anxiety / depression / etc, or need a consusltant neurologist for epilepsy / parkinsons / etc
All the patients might not need to see the consultant (can have appointments with a clinician who isn't a consultant) but the consultant with the relevant specialism to the patients condition would sign-off at important stages