This way you can easily update your scenes with the editor between the sessions: like to replace all items with their burned variants after our group of pryomaniac adventurers were raging in the last session. I already hear the laughter when starting the next session and players see the evidence of their destruction.
If you continuing the session - its just enough to load savegame with it. All changes done to the level will be kept in scope of the saved session. I.e. if you started a session with players - saved - then loaded - everything will same as when you saved - so all destruction and flames and blood everywhere all will be kept. Even if you go away from scene and returned to it later - it still will be in the state you left it.