Don't really think the hub adapter is necessary, once you cinch and torque the lug nuts down (to 100 ft/lbs) the wheels become lug-centric vs. hub-centric anyway. I have the hub adapters on my winter wheels... I think they really only make initial fitment on the rotor/hub easier.
While not totally necessary, they aid in making sure the wheels are centered properly. Without the adapter, wheels should be tightened and torqued OFF the ground. A lot of people forget that part. The adapter makes it a bit easier and more "foolproof"