Originally Posted by joe_padavano

No, it's actually torque-limiting. The torsional wrap-up of the stick (or long extension) absorbs the torque from the impact wrench. If the impact wrench were continuously rotating, the sticks wouldn't work - once you wrapped them up, the torque would again be transmitted to the nut (until the stick broke). Since the impact wrench has discrete impacts, so long as the angular deflection of the wrench is less than the wrap-up of the stick, the nut will not tighten further.

Originally Posted by Octania

Great explanation Joe P.
Now I trust that device

The longest extension I have used is the 4-ft unit I made for trunk latch removal via rear seat. The longest I have used that twists and bounces is a 12+12+6 or so plus a swivel socket for the trans to engine bolts from waaaay back where you can swing a ratchet.