I agree with the desirability of owning and using torque wrenches, particularly for the new bike mechanic. An experienced mechanic with years of working on a variety of bikes can get along fine with out one (e.g. Sheldon Brown) but the new guy has no idea how tight things should be or what the proper torque feels like. It is likely you will never get bottom bracket cups or crank fixing bolts tight enough and will probably over-tighten small bolts without one.

Bobby Lex's comment about the intolerance of very light and exotic components to improper torque is right on.

You don't need anything sophisticated like a "clicker" or electronic wrench. A plain "beam type" as shown above is fine for any bike work since you can always see the scale.