If, when on different levels, the same follow behaviour is desired, then the follow checkboxes must be checked on those levels as well. By separating the follow switching, it is possible to have sources follow only when switched from a particular level. If the switch is from a different level, then individual levels can be switched.
On the destination side, the check box indicates that this destination ignores follows from different levels. If checked, assignments from other levels will not follow, regardless of the source follow check boxes.