My guess is that's because of their long experience as mechanics, where they have gained a pretty darned good sense of the appropriate torque required for different parts. I'd bet that 95% of shade-tree mechanics (like me) never gain enough experience for that to happen. A torque wrench eliminates the guessing.

On an engine, absolutely use a torque wrench on assembly.

On a bicycle, you can have a good sense of feel when you go past snug and into tight. Cable ends, very important to be tight but using small wrenches is all that is needed.

The main point where a torque wrench is needed is when you are clamping on carbon. In that case, the spec is very important because over tightening can crush the carbon and cause a failure. That said, common things like seatpost clamps and stems on carbon parts almost always need something like 5 or 6 nm which is easy enough to do by hand. In the shop I was at, we had pre-set Bontrager tools laying around and it was really easy to grab those every time we did a headset adjustment and needed to tighten the stem. If for some reason I had to do it on the side of the road, doing it by feel wouldn't be too far off having done it hundreds of times on various bikes.

That said, there are lots and lots and lots of bikes with alloy bars, steerers and seatposts. At that point, precise torque specs aren't required as much as common sense is needed to not go ham fisted on it and to make sure each bolt has even tension on things like a stem. 90% of the time it's tightening a stem on a carbon steerer or clamping a carbon seatpost, and in that case it's super duper easy to just grab the preset tool I mentioned earlier.

The only time I remember pulling out a real-deal torque wrench was generally for Shimano Hollowtech cranks (and there it's less the crushing of the spindle issue as much as it is making sure both bolts have even tension without going so tight as to over stress the bolts), Campagnolo ultra-torque cranksets (with a single bolt holding it together, you kind of want to make sure i'ts done right), and weird aero seatpost setups where you couldn't use the preset tool due to clearance issues.

Especially that seatpost clamp!

I've never seen a handlebar or seatpost with a stamp indicating maximum clamping force.

5-6nm MAX is commonly printed on stems... but what does a stem know about the clamping force needs of a handlebar? Traditionally, torque specs are for MIN torque, as in, "part must be tightened over this torque to be safe/effective". Any time you are clamping something that specifies a MAX torque, you should tighten until snug, then slowly increment the torque until the part holds under load and no more. You are looking for the minimum amount of torque that will do the job. You are not trying to reach a preset number. There is no need for a torque wrench in this process, much less one that is preset to the maximum torque specified.

I would get the ritchey one that is fixed to 5 NM and only costs $19, It's all I needed for seatpost clamp, stem and braze on front derailleur.
for crank arm you have to be a serious nut job to damage anything....

I have worked on my own bikes for a long time, and I've never used a torque wrench. Nothing has ever cracked or fallen off. :-)

But then I've never owned carbon. Just steel and aluminum.

If I ever did buy a carbon bike, I'd definitely get a torque wrench.

necessary?....is it necessary that I drink my own urine, no, but it's sterile and I like the taste.

Myth: https://www.sciencenews.org/blog/gor...ither-rest-you

If you have been here for some time you will have seen the posts "I only tightened it to the spec and the bar or post crushed". Just tight enough is my target.

I would use a torque wrench there are times if you over torque it can be an issue. The FSA recall comes to mind when thinking or the need to correctly torque.

FSA GOSSAMER BB30 RECALL NOTICE - FSA