Originally Posted by
ScottCommutes
You never need a closed-end wrench, but at high torque it is a better practice when you can because you are grabbing all six points.
Actually sometimes you do need a ring spanner, because they have narrower shoulders than an open-ender and can turn 30° at a time. There are jobs on cars where you should be removing a major component for access, but you can avoid that if only you could turn those two hard to reach bolts ...