Yes, most Doctor's recommend Propecia (Finasteride) to halt any further loss after you have had a hair transplant. Those who are good reponders, having tried Propecia before a hair transplant, sometimes can avoid having one altogether. Others too far gone that need the hair transplant use it to stave off further loss after having one.
male pattern baldness is progressive just like Hairbank stated. If you have natural hair left affected by DHT, then most of us continue with finasteride. So finasteride is not for the terminal or transplanted hair not affected by DHT.