I agree with several that have posted. There has to be a line.
Question: The Bag Guy in the scene has been stabbed by the swordsman in the group, shot twice by the marksman, he is looking pretty bad, but is still standing.
Does the Wizard throw a minor bit of magic to "knock him out", because he is worried about killing him?
or
Does the wizard unload with max force to be sure the guy is finished off, since (according to the rules) he doesn't have to worry about killing him?
Part of the thrill in the books I enjoy is the temptation of power that magic gives. You have to use it responsibly, you cant use it to solve every problem, and if you do over use it, or use it to solve problems it shouldn't be used for bad things happen to you.
Ultimately, its up to each group, each player. But I would like to see both GM and PC on the edge of the seat when using magic to hurt someone. Yeah its cool as heck to throw fireballs and lightning blasts around at a whim. But what happens when the building catches on fire, and the power grid of the city block shorts out. How many disruptions are going to occur before the over zealous wizard(s) are hunted by the authorities as terrorists, and the wardens as rogue warlocks?
So start with B but if the players abuse it, then switch it to A. They will have to learn to pull the punches so you can switch back to B. Perhaps there is no clear defined answer on this. But abuse is a two way street. Player and GM should share the responsibility.