I'm 8 weeks out from my surgery (BSSO, Lefort 1, and genioglossus advancement), and was not fitted with any kind of splint. I was, however, banded from Day 3 through Week 5. Bands made a HUGE difference in my case. I could be atypical, though?
When I woke up after surgery, I could more or less open my jaw as wide (if not wider) than I could before surgery.
For the first three days (I was in the hospital for 4) I was barely able to get down any liquid, even my meds. Once the bands were on, it was SO much easier - they helped guide me to "feel" how to use my mouth when I largely couldn't feel, well, anything.
It does seem kind of ridiculous that these tiny rubber bands could have an impact on something as powerful as your jaws, but I can assure you, they were absolutely necessary. After week 1, my bite wasn't quite where it should be, so my surgeon doubled up two bands on each side of my mouth and anchored them on my IMF screws at a sharp angle. This helped me to learn how to properly hold my new jaws at rest, and after another week, my bite was exactly where it should be.
Something to keep in mind - my bite was more or less perfect before surgery, so I think that resulted in fewer bands and less restrictive placement than what would be typical for someone who required orthodontics before and after surgery.