The reason this is important.
When items are placed on either of these layers the display of these items can only be changed by removing them from these layers.
This defeats the display status of the other layers as intended.
If models are checked into common-space with items on these layers(hidden/shown), then the display of these items is no longer as intended by the layering schema.
This will negatively impact other users as they are no longer able to predictably control the display status of model items.
