Hair transplant results are meant to be permanent and should last a long-term , usually a lifetime.
To get a result that will stay for many years, clinics need to follow certain set procedures and technique.
Only anagen grafts should be harvested and placed meticulously so as to have a high yield of good quality of follicles. Longterm results cannot be obtained if all available grafts are being harvested. This is more true of FUT technique in which cherry picking of grafts can never be done.
The out of body time affects the viability of grafts and needs to be minimised.
Any graft not surviving will affect the resulting density.
Any grafts which is from a miniaturising zone will fall off as per its genetic encoding and will also affect the eventual long term density.
All such feeble grafts can be however sustained by long term Propecia intake, but medications like these are not without side-effects.
This philosophy may entail lesser number of grafts and affect commercial viability in this age of discounts and as a corollary large number of grafts being quoted.
You can see many such cases of our results at-
https://www.youtube.com/channel/UCZ3GsvIndDGDFZwTVVxAvGQ?view_as=subscriber