I'm currently in Act 3 on my second playthrough (the first I stopped a long time ago at lvl 10 because I was annoyed too much by some game design), being lvl 12, and I have to say that I never felt the urge to use control spells as well as top level aoe spells that frequently. I usually try to solve problems with cantrips, crossbows or concentration spells which you can use for several rounds. Using control spells often would need more spell slots then using aoe if you applied them generously to many NPCs. On the most important NPCs they often don't work. Or do they?
There were some difficult fights, the owlbear (I had to run away because the two damn siblings turned on me), the Gith patrol (a fight before I realized that initiative is all, they killed two and reduced 90% and 50% health of the other two before I could even roll the dice), Bernhard (I underestimated his aoe), the Gith captain (not the inquisitor) in the creche (very bad luck with the dice), and above all, Grym (first time to play it in Honour mode was a bad idea), and then when all the soldiers and some steel watchers became hostile in the Kontor because I forgot that reading the mind can make people mad. Maybe a control spell would helped me in some of the fights, but can you control Grym for example? I was too panicked and busy to try.
Currently I try to solve the Ethel problem in Act 3 once and for all; I was badly prepared for the encounter, only tactical retreat helped me (I didn't know anything about the fight before start). I will try to control her maybe as an alternative approach next time, before she creates another million of copies. If it helps, I will praise control spells forever.
