Here's just one persons thinking on those ring gear spacers/sleeves. This is Hybrid Z, so most cars have quite a bit more torque than stock. In my mind this large amount of torque may move the ring gear as shown in my rather crude illustration below.
Now, what that illustration shows may or may not happen, but these spacers/sleeves will prevent that. Are the spacers/sleeves worth that peace of mind? In my opinion, yes.
Also, the ones I made were cut to the correct length, just even with the bottom of the chamfer on the carrier as shown in the above illustration, so you guys that purchased a set, don't worry about your ring gear not being true.
EDIT: D' OH! Jon posted his message while I was writing mine.
!M!