I have learned that some bike and component manufactures have specific torque specified and others don't.

One Bontrager stem specifies 5nm and another Bontrager stem specifies 8nm. One stem I had, I think it was a Salsa stem specified 11nm.

There was a time when torques were not specified, as far as I knew. I simply tightened what ever it was to what ever 'seemed' right. With experience, sometimes painfully, I have learned a certain feel for too tight or too loose but often times I still don't tighten to a specific torque. Experience has been a good teacher and I don't usually have any problems with too tight or too loose.

How much does torque matter if no issues are encountered by the rider? Is there that much difference between 5nm and 8nm? Do you torque every bolt and screw?

If no torque is specified, how much torque do you use? Is there a general guide line or chart somewhere with generalized 'best practice' torques for different components?