[twoodfin]

I can imagine at least three rationales:

- Avoid "manager shopping", wherein a low performing employee transfers from group to group until he finds one that doesn't recognize his lack of competence. Similarly, communicate to the low-ranked employee that his only path to redemption is with his current group.

- Encourage effort from employees who are dissatisfied with their current group. Continue to perform or you won't be able to switch.

- Discourage managers from handing out worse reviews to team members whom they'd just like to see leave the group, as opposed to genuinely poor performers.

But I'd love to hear the real reasons.