I have been wrenching on cars, motorcycles, and bikes for a long time. Never used a torque wrench on a bike and never had a problem because of it. But as has been said already if you are not confident in your "feel" of how tight bolts should be then get a torque wrench. Also as "merlinextraligh" has pointed out the recommended torques may be more than is required for the job. Bicycle bolts are not under heavy cyclic loadings like a connecting rod bolt and as such fatigue failures from under torquing are not a problem.