In most cases a urinary catheter is REQUIRED without exception due to the fact that the majority of orthognathic surgeries are done under what is called Hypotensive Surgery in order to reduce blood loss, which can be significant. This means the Anesthesiologist will drop your blood pressure to a level that it would normally never be while you are awake. The procedure is very safe, but only if safeguards are in place, like for example, a urinary catheter.
You may ask, why? Simple actually.....
Your kidneys are your MAIN blood pressure regulating organs in your body (long term), so they are very sensitive to any kind of change in it. If your blood pressure goes too low, your kidneys don't get enough blood flow, and could potentially go into failure. To monitor that your kidneys are getting enough blood flowing through them, urinary output is CONSTANTLY monitored to make sure they are working 100%. If you're not producing enough urine, your blood pressure will be adjusted accordingly. While you're in surgery, they will be giving you IV fluid. So what goes in, has to come out so they know how efficient they're working.
So my personal opinion; I think it would be better to be safe and deal with the very short term inconvenience of a catheter than opting out. I don't think a good surgeon would do hypotensive surgery without it anyway. Besides, if you're going to deal with the difficult recovery of ortho surgery, is a catheter you have to have in for 1 or 2 days max really ALL that bad?