Currently, there are 3 default layers, the Token layer (For visible objects that are frequently selected or changed), the Map layer (for visible things not usually selected or changed at game time), and the DM layer (a catch all for things only the DM can see or interact with). I think it would be very beneficial for the DM layer to be changed to two layers, the DM map and the DM token layers. This way, the DM can have notes, icons and other information visible to them, but which is separate from invisible tokens which are frequently moved or changed. I can say from experience that it can be very frustrating to be trying to move a token representing an invisible enemy and accidentally move a DM map element or note.