All the doctors I go to have a partner I never know who I will get but I trust the whole of the practice. I pick my doctors from word of mouth, good results and how good the staff is from the front desk to the cleaning crew.
If a doctor has been in practice for a long time I'm sure he knows the ropes of how to hand pick the right people to do the right job. To expand a practice includes adding new staff that has been trained to your own perfection.