(For the sake of this topic we assume that both techniques are performed competently)
Deciding on a HT is a hard decision; the technique used will play a major factor in your long term happiness, goals and intentions. Both techniques have their pluses and negatives and so it is important to ensure you choose the correct technique for long term planning and getting the most out of your donor.
FUE, the donor surface area is opened to the maximum but that does not mean there are more follicular units (FU) to be taken in comparison to FUT. Every FU removed will reduce the density, the more removed can noticeably drop the density and impair the donor for future procedures, FUE or FUT. Assuming an average density around the safe zone of 80 FU cm2 if the extraction pattern is spread and no areas are over harvested around 4000 FU could be removed, this will drop the overall density down by around 30%, leaving a density near 60 FUcm2 in the donor, and this would then be considered low density on a virgin scalp.
To sustain the density in the donor FUE is better suited to lower graft numbers, with an educated extraction pattern, no over harvesting or partial shaving , then the density change to the scalp can be minimal, if the candidate has an average to good density to start with then around 1500 grafts can be removed and hardly affect the overall density. With more advanced patterns of baldness FUE starts to be less of an option over one or multiple procedures; grown out results of 3500 FUE plus grafts are not the norm and require very good donor characteristics. If high FUE numbers are performed in one procedure there is a greater risk the yield will not mirror that attained through FUT; a real medical concern of large FUE procedure is the effect on the body to heal multiple open wounds created in the recipient and donor area simultaneously and how effective the body can sustain and heal whilst not impairing the scar healing in the donor and yield in the recipient.
A possible exception to the FUE rule on larger hair loss pattern candidates is when there are limited goals, not looking for total restoration, lower density placement due to specific hair styling, or the “5 o’clock shadow” look for those who want a high conservative hair line to frame the face and frontal area and intend to keep their hair short/shaved; but this is not the normal HT candidate and very important that goals and long term intentions are discussed and understood by the candidate and the doctor.
FUT will remove a hair bearing strip of tissue and therefore effectively the hair density has not changed significantly in the donor as the surface area is removed opposed to hairs removed from the surface area. The scalp laxity allows for a strip to be removed without causing any long term tension and over time the skin heals well. There are limits to how many times this can be repeated but in good conditions 2-3 times and with good skin healing attributes it will be able to englobe the existing linear scars to leave a single line rather than multiple wounds.
FUT removes a high concentrated number of FU from a relatively small area and they are removed still in their natural state of high density on the strip; 4000 grafts in one procedure is an achievable number in the majority of candidates unless the donor density or laxity is particularly weak. For long term planning and high NW stages FUT makes it easier to plan and cover with a good density the largest surface area possible. FUT does have the disadvantage of leaving a linear scar so more visible signs a surgical procedure has been carried out but the advantage of being able to move a greater number of FU either in one procedure or multiple procedures compared to FUE and still sustain a similar density as before in the donor.
Conclusion, the advent of FUE means no need to be left with a linear scar for a relatively small amount of grafts placed so from a cosmetic angle it allows the patient to have an HT with little to no obvious signs that a HT has been performed. FUE due to the technical demands of the procedure being labour and time intensive as well as the medical healing and yield concerns is better suited to smaller sessions for the majority of hair loss sufferers. If the pattern of baldness is high and the goal is to cover a large surface area with a natural looking density then FUT would be the sensible and obvious choice to achieve the best result for the candidate.
The combination of both techniques can be utilised to ensure the original scar quality healing is maintained and using FUE to maximise the donor extraction zone, whilst still allowing the potential for future surgery using both techniques if need be. Combining the two techniques allows the best attributes of both to be used, maximum movement of grafts and opens the donor zone, concentrated high number of grafts from FUT and harvesting outside the traditional safe zone with FUE. What has to be remembered though is with either technique they are both scalp/hair characteristic changing in their own way, hair is being removed and there will always be a consequence to this, be it loss of density or laxity or scarring.