I never really put much thought into NPCs; usually I operated under the "name/nameless" rules for NPCs. In general, if any given NPC is referred to by a name, as in "Bob" rather than just "the waiter", then that NPC is at least important enough to give priority (but not necessarily absolute) control to whoever introduced that NPC, or the GM in charge of the RP, whichever is best for the situation. Conversely, if somebody introduces an NPC without giving them a name, then that NPC is probably unimportant enough that everyone involved in the RP can dictate their actions and reactions moderately freely.