Saint Sheldon had an opinion on using a torque wrench ...
Experienced mechanics will strip threads as part of the learning process. After you've stripped a few, you get the "feel" for what a given thread diameter and depth of engagement can take. This is a very worthwhile skill to learn.
Bicycles are meant to be user serviceable without needing a lot of exotic tools. Nobody carries a torque wrench for on-the-road repairs, and I never heard of anybody using a torque wrench on a bike before, say, 20 years ago. (note: original post from 2001)
A torque wrench is like training wheels for a mechanic. If you want to become a competent mechanic, you shouldn't be afraid to strip a few bolts in the learning process.
Sheldon "Doesn't Do It By Rote" Brown
One area where I’ve found a torque wrench helpful is the left crank arm, it helped me get a feel for how much leverage was needed. This is an area where learning about too little torque can be destructive. A loose crank arm will ruin the press fit of the crank arm on a square taper bottom bracket.
I think more important than a torque wrench is proper lubrication of threads and underside of bolt head. All threaded fasteners must be lubricated for them to be tightened properly. He lays out the lubrication checklist here ...