Oh...boy
Okay crash course in fastner technology (anybody with engineering experience jump in at anytime!)
EVERYTHING has a property refered to as modulus of elasticity. Your bones, a toilet seat, a window, a rubber band, carpet, paper, ect
This describes how much deformation a material can withstand before it loses its mechanical properties or becomes permanently distorted. I believe these are refered to as eleastic and plastic deformation. Once the the material has exceeded the elastic deformation range it then enters into plastic deformation and exhibits a loss of mechanical properties and is unable to return to its original form.
This property is useful when it is applied to fastners, like a bolt, nut, stud, ect.
Where based upon its dimensions and physical properties the fastner is stretched a specified amount so that it does not exceed its range in plastic deformation, but instead tries to snap back into its orginal shape (much like a rubber band tries to contract back into its orginal shape when stretched). This is what provides the clamping force which allows the fastner to remain tight.
There are two ways that I know of to determine the correct amount of stretch needed to reach the desired clamping force nessecary to maintain a tight fastner. The one most people are used to, a torque wrench, the second being a stretch gauge. the former is used to reach a specified amount of torque which will stretch the fastner to a specified length range. The latter actually measures this stretch and is considered the more accurate of the two methods.
If the fastner in question is not torqued (or more correctly stretched) to the reccomended specification, then the pressure will not be sufficient to adequately maintain a clamping load on the fastner. The end result being fastner failure and the collatoral damage which can be associated with a loose bolt or nut.
Converesly if the fastner is stretched to far it will lose the mechanical properties nessecary for providing and maintianing this clamping load ultimately resulting in fastner failure (think about this the next time a gorilla in a uniform hammers the lugs down on your car with an impact wrench until the gun quits moving).
In every instance, friction can affect this requirement (hence the use of a lubricating agent when torquing the rod bolts). However some fastners are designed with this requirement in mind (most obvious are lug nuts, which generally should not have a lubricant applied).