Power becomes more important with maneuvers and blocks because you defend against the POWER of the spell.
Even targeting maneuvers! The enemy defends against the Power of the Maneuver NOT the control roll!
I will find the rules for this in the book...
So, if you're going to do lots of blocking and maneuvering, you should boost your power a bit. Of course, you still have to control this or risk back-lash, so I still think discipline is important.
Performing maneuvers is a little trickier than
attacking and blocking. By default, pulling off
most maneuvers requires 3 shifts of power, but if
the target has an appropriate resisting skill rated
higher than Good (+3), that skill total determines
the required number of shifts.
So technically, the person doesn't defend, the difficulty is their skill or 3, whichever is higher. I always let the enemy defend.
If they fail by no shifts, the aspect is fragile, if they fail by more than 1 the aspect is sticky. (usually)