I was given advice that while changing a tire, you should loosen the nuts with a lug wrench instead of using a torque wrench. The torque wrench should only be used to finalize the tightening. This person told that the torque wrench might be at worst damaged if it is used to loosen the nuts. Why might this be true? The torque wrench is used to tighten the nuts to the final tightness, so why cannot we use it to also loosen the nuts?
Because it's not designed to loosen them. It's a cardinal rule of torque wrenches. You will screw up the calibration by doing so. A torque wrench is meant to be a precision instrument, not a breaker bar.
One way it could be ruined quite easily is if you have a stuck fastener or one which requires much more torque than the torque wrench is capable of taking (or applying if you were tightening it). If you put 350 lb-ft of torque onto a wrench which is only capable of 250 lb-ft, you will destroy (or severely mangle) the mechanism which accurately reads the amount of torque applied. When you start to try and loosen a fastener, you really don't know what it's going to take to get it off.
What this boils down to is to use the right tool for the right job. Using a torque wrench to loosen a fastener is akin to using an ax to swat flies. It just isn't going to end well. Get a breaker bar and save your torque wrench for what it was designed to do.
A "breaker bar" is much cheaper than a torque wrench and will take much more abuse.– jwh20Jan 5, 2022 at 20:54