Yeah, basically it measures the high and low spots of the rim and tire under road type conditions (it puts pressure on the tire). It will then tell you where the high and low spots on tire and rim. You then match the highest point on the tire with the lowest spot on the rim.
You want a tire to have no more than 8lbs of road force. When your done, if it does then the tire is garbage.
It is basically suposed to get rid of that vibration from a shifted belt or get the minor inperfections out of the tire.
I dunno if that makes any sense...