What is your opinion on a combined FUT + FUE surgery to maximize the number of grafts harvested?

FUE is just a harvesting method.  It does not relate to results.  If you want to keep your hair very short you may want the FUE.  If you combine FUT and FUE you will have a shaved head with a long scar and lots of round dots during recovery.

Doing an FUE and FUT/strip combination procedure is a great option when you need to maximize graft numbers in 1 surgery. With that said - it is crucial you find a highly skilled hair restoration surgeon who is highly experienced in both methods. That is of utmost importance for a successful outcome. 
There are many complications that could potentially arise if choosing the wrong doctor. From scar formation after bad FUT/strip procedures to over-harvesting and using large punch sizes in bad FUE procedures - we've seen it all and I've had to do many scar revision surgeries over the years to correct careless mistakes so please do extensive research, choose wisely, and ask many questions at the time of your consultation. 
If you find yourself in the hand of a reputable surgeon with an artistry for hair, an FUE/FUT combination can yield amazing results! 
Make sure to read and look at the photos in the link I've attached on a botched FUT surgery we corrected using the combination of both methods. 

As with every procedure there needs to be careful evaluation of the donor supply.We have done a number of “hybrid” procedures and they work very nicely.The best application is on redo procedures where the donor supply is more limited and we are trying to maximize the number of grafts obtained.

That's a good question.  For one, the strip method (FUT) will leave a linear scar across the head.  For some people, it isn't noticeable.  For others, it is quite obvious.  With FUE there really is no need to put yourself through a strip surgery, even if the goal is obtain more grafts.  There comes a point, and this could be debated, that after a certain amount of follicles, the law of diminishing returns comes into play, and one case "waste" follicles for further use. In addition, radical, large sessions with 3,500 + follicles may yield a lower graft survival based on several factors including but not limited to fatigue and prolonged graft explantation.  Your best bet is to get an honest eval from a reputable doctor and develop a "plan of action" since hair loss is generally a chronic situation.  The goal should be to maximize your "bang for the buck" as they say!

For larger sessions of FUE there is possibility of donor depletion and so some doctors are reluctant to do larger fue sessions. At the same time with FUT there is a possibility of tension after harvesting in larger sessions which may lead to scar formation. To minimize the possibility of causing scar fromation in fut and donor depletion in fue in larger hairtransplant sessions, a combination of the two is a very good option. You need to see a good doctor who performs both, otherwise if the doctor only performs one or the other technique , they usually do not offer it and are against the idea. 

The number of grafts depends upon the size of the recipient area you want to treat, the thickness of your hair shafts and the donor density of available hair. For FUE, there is an absolute limit to the number of grafts that you can harvest with FUE before you develop balding in the donor area and a see-through donor area that you can’t hide.  I can tell you that few men can support more than 3500 FUE grafts before becoming bald in the donor area so much so that anyone will notice it. IF you are Asia, or African, or middle-eastern, then most likely you can’t even support 3500 grafts. A good doctor knows how to assess this with proper donor density measurements of your original donor density and then there are known calculations that follow this information once it is in hand. Combining FUE and FUT is not an unreasonable way to handle the numbers you might need in a single session, so see a GOOD doctor.