Dan,
They split the jaw for access to the tonsil, and to complete the flap reconstruction. The scar down the side of "our" necks is from the dissection.
Mica, in addition to what we have done you need, to a degree, trust your doctor on this one. The neck dissection is nothing compared to the tonsil surgery and the added insurance of a pathology report would be priceless. I had a functional neck dissection with 30 nodes removed and have suffered no real rang of motion issues. My final observation would be that a reoccurrence can also result in some far more serious neck movement problems, go with the most aggressive approach tolerable the first time around!
Good luck,
Glenn