One very important reason that surgeons don't lie overweight people on the table is the fact, that it is hard to suture reliably in fatty tissue. Sutures tend to break out from such tissue. Furthermore, fatty tissue has very poor blood supply and because of this, it tends to poorly heal. Poorly healing issue with poor blood supply is prone to develop post surgical infections that might be very complicated and expensive to treat, and might end up with lots of ugly scars.
We always recommended that candidates for voluntary surgery should be as lean as possible!