Torgue wrenches vary greatly in accurassey. Practical Classics did a test on the smaller ones, what they found was that a lot where accurate in the mid range, but few where accurate in the lower ranges, which is where you will need it for the bike bits which are critical to easily stripped threads!
I agree that it is beneficial to develope a 'feel' for tightening up the variuos parts of bikes. Relying on an innacurate torque wrench (perhaps one from argos or somewhere similar) to tighten up a 5mm bolt into an alloy thread could well mean a stripped threa while waiting for that click. A skilled mechanic should have a feel for just tight enough and a bit more to lock.
Torque wrenches are very critical in automotice engine building and such like, where you are mating large flat faces together under a lot of pressure and subject to warping, such as alloy cylinder heads.
I use torque wrenches for vehicles regualarly, have never used one on my bike.