The mobility transfer policy requires to notify the manager before conducting the second round interview - question

So the current mobility transfer policy requires you to notify your current manager before the second round interview to be conducted - why is this required? I understand it’s better to notify the manager before you want to do transfer on the firm’s procedure standard, but the thing is if there is any action item (approval/vouch/questionnire etc) required during this notification step, and the manager has to approve/vouch/fill out the questionnire) before you can move forward? Monkeys in BBB, What’s your experience like (if you had pulled off the process or involved in the process before)?