Are torque wrenches worth it?

I think there is some confusion here as to what torque wrenches measure. It's simply the rotational force being applied to the head of the bolt. That does not vary by +/- 25% error.
I don't believe anyone in this thread is confused, but could you please expand on the last part? I have no interest in the source I quoted, so I am happy to see a qualifed refutation.