From the interview Swen made with RPGCodex (not only about GM mode)
http://www.rpgcodex.net/content.php?id=10670
The GM mode has nothing to do with singleplayer, it’s purely for multiplayer. In Gamemaster mode, when you see the backend, there’s no scripting in it whatsoever. It is really something that has been made to allow the GM to modify the world in real time while you play the session. He can control characters, he can create items, he can create surfaces, he can change the weather, change the ambient music, etc.[...]
You should have a read guys. That may answer a few questions.