Nail said:
Couldn't we apply this to every charm spell?
Hmm. That's a good question... what does 'exercising control' mean in the case of, say, Charm Person?
"You can try to give the subject orders, but you must win an opposed Charisma check to convince it to do anything it wouldn’t ordinarily do."
I'd say that's certainly 'exercising control'.
"This charm makes a humanoid creature regard you as its trusted friend and ally (treat the target’s attitude as friendly)."
Is the persistence of this regard, already in effect, an exercise of mental control?
Let's take a hypothetical situation. I'm new in town, and I don't have any friends. We both grab our morning coffees at the same cafe; you've seen me a few times, but you don't know me - your attitude is Neutral.
I cast Charm Person on you - your attitude is now Friendly. We hang out for the day - go bowling, have lunch, catch a movie, chat about inconsequentials, and get to know each other. A good time is had by all. After twelve hours, the spell expires.
What's your attitude towards me after the spell expires?
-Hyp.