Just wanted add a few comments because the nature of your question should inspire you to really research the full effects of MPB which is a progressive disease. Genetic hairloss is a lifelong event for those who have it and it can be difficult to predict the rate of prgression as well as the extent of loss that one will experience.
That's where reviewing both sides of one's family history becomes helpful. If one has family history of MPB and reaches the advanced classess, generally Norwood 5 through 7, that's a sign that you may progress to the same degree of loss.
What I find oustounding every day are those men who have their rate of progression slow down considerably with the use of finasteride or dutaseride, and for some, adding minoxidil. My maternal grandfather and uncle had extensive hairloss up to class 6. Neither of them had used any hairloss drugs. I did not have the opportunity to use finasteride until I reached class 4-5, however, 12 years later, I still have not noticably lost any more of my native hair subject to DHT. My uncle is now 79 years of age and still a class 6.
It is for this reason why patients need to get additional procedures. Subsequently, there are very few patients who get by with one procedure. Some simply do not have MPB and simply want to lower a hairline. And I agree that the preservation of available
donor is absolutely critical.
Please note that I said [I]available[I] donor. Some of the donor zone can be miniturizing which is proof some of it is DHT receptive and not to be considered terminal hair. I would think that any HT surgeon would inspect for this on every patient prior to surgery. My point is that every patient must plan for the needs at present AND the future as hairloss continues. Once started, the patient is committed to future procedures.
Some docs will state that they solidly believe moving as much hair as possible in the first session is the best approach. They will state that the virgin scalp is the most ideal environment for the best yields because the blood supply has not been previously compromised with scarring from prior procedures. I don't necessarily completely agree with this because ANY procedure is going to compromise the exisiting environment. It is true however that the more incisions created, the more the recipient area's blood supply is compromised.
The only other time it would be the motive is because the doctor is trying to get as much revenue as he/she can. Do you think that might ever be the case?