And even a closed door in a residential building can slow things down enough to make the difference between life and death. This is why the fire service encourages people to sleep with their bedroom doors closed and to have a smoke detector near said bedroom door.
The downside to a heavily partitioned building, especially a very large building, is that it may become a maze that is hard to exit, and lots of doors between different areas slightly increase the risk that somebody will have a brain-fart and lock/chain doors that should never be locked, or otherwise do something that effectively traps people inside. Note to everybody: never chain/lock/barricade a door that must be used to exit a building in an emergency, in such a way that it can't be opened from the inside.