SkieWhy does each group have one policy and one app list?
Each group in Skie has exactly one policy and one app list attached at a time. That keeps the answer to 'what rules apply to this tablet?' simple and checkable. If you need a different mix for some students, you make a separate group rather than layering several policies on the same one.
The group is the unit that devices belong to, such as Class 8 B or a hostel floor. Attaching one policy and one app list to it means every device in the group has the same behaviour, and a teacher or admin can say exactly what that is without tracing a pile of overlapping rules.
It also makes changes predictable. Swap the app list and every device in the group picks up the new apps on its next sync. Swap the policy and the hardening and hardware switches change together. You are never guessing which of two competing policies won.
Rules still flow down from the organisation to the school, branch and group, and the most specific level applies last. So an organisation can set defaults, and a group's own attachment refines them. The effective policy view shows the final result for any group or device, which is the quickest way to confirm what a tablet is actually following.
If you find yourself wanting two policies on one group, that usually means the group is really two groups, for example students who need Chrome and students who do not. Create a second group, attach the other policy, and move the students across, singly or in bulk. A schedule can switch app sets during the day without changing the attachment at all.