yeah those are called hub centric rings. basically they help the wheel mount flush onto the wheel hub so you don't get any wild vibration and break your studs off and lose a wheel driving down the road ;)

hub centrics don't do anything with balancing. right now the industry standard in wheel balancing is called a spin balancer. it mounts the wheel on a post on the side of the machine and you slide a cone down the post to fit flush into the hub flange of the wheel. than you take this giant wing nut lookin thing and spin it onto the post so that the back of the wheel seats on the balancer flush simulating a mounted wheel. hub centrics are to help with clearance around the hub so the wheel fits on nice and tight.