There is no worse mission than protect-the-weak-and-dying-masses.. A quest could be to get a person from point a to point b, while dm sets up (logicall) encounters with creatures.. Perhaps the person being escorted is a "key" (carries one) to open certain door in certain dungeon to get a certain object to slay a certain generator which creates a certain nasty strain of creatures..
It is possible to play an NPC.. with that dm command: possess. I've done it before, fooled a player into thinking I was an NPC. That command does still exist, right? It had a lot of bugs, though, i remember.
I can't imagine that this command was created to fool players. This certainly doesn't make a good impression to newbies and therefore doesn't seem proper behaviour for a DM.
IMHO it should only be used for some serious roleplaying and not to fool others.