I don't know, good question, but they seem to move the mesh around in relation to the centers. If you move them too far things get weird, but they can help. Took me a long time to track down why they show up once in awhile. The problem is, once you think about it, a conforming item has to use the same centers as what it is conforming to, else the fit would vary if the joint was bent, but what happens if your mesh is a little off in location? You can't change the centers, as above, the offsets seem to be for adjstment here- most of the time you don't need 'em, incidently, but putting high-heels on flat feet is a special case.