I used to do a lot of mechanical work on cars as well (before I started disliking them for environmental and social reasons). I used a torque wrench for practically everything I did with cars.

Now that I'm a bike mechanic, I only use torque wrenches when there is a danger of crushing something; most notably, carbon fibre. I know when something is tight enough not to come loose from experience, and I can feel when a bolt is about to strip (either the threads or the head itself). The feeling in the bolt dramatically changes at that point, from one of solid resistance to gentle acquiescence. A bolt will always increase in resistance as tension increases, due to increased friction, unless either the head or threads are stripping. So if you're tightening something and it suddenly becomes easier to tighten, back off

Carbon fibre, on the other hand, gives no warning when it is about to crack. I haven't cracked any carbon fibre parts yet, but I don't intend to either. So a torque wrench has obvious application there.