Yes, you can have multiple floors set next to each other and use Fog of War, but there are so many situations that BEG for multiple layer functionality. Just a few things to consider:
TREETOP/CANOPY COVER: Being able to place your token "under" the tree canopy making it clearer that they have cover from flying creature sight, etc. would be great!
MULTI-LEVEL FIGHTS: Having multiple maps only works well when each floor is solid. What happens when the ranger goes up to the Inn balcony to shoot DOWN at the fight? Makes for a really difficult time when their map no longer shows where people are, and having to duplicate moves across multiple maps gets ridiculous.
NAVAL COMBAT: Have someone in the crow's nest as a sniper? it would be useful if you could have those sails, etc "covering" people below to help figure out line of sight, wouldn't it?
URBAN ENCOUNTER: Have someone inside the building, in the street, on the second floor, and someone on the rooftop/balcony? wouldn't it be great if you could layer them up so everyone is on one map, but when someone moves out from under some cover, the people above can see it? AMAZING!
If this was a Pro feature alongside dynamic lighting, I would subscribe in a HEARTBEAT. I cannot express how sad I became when I realized that the GM layer was only visible to the GM. I have found the GM layer to be invaluable in its own right, but layering trees, etc to give a realistic perspective to my map prior to my first session, just to realize my players were not seeing ANY of it, broke my heart a little...
