Different levels of detail are put in the model depending on what you are interested in learning.
For example, if you are designing a Sheetmetal structure and plan to use screws at specific locations, a common modeling approach is to use a Fixed Joint to connect the hole in one sheet to the hole in the other sheet. Use one Fixed Joint for each screw in the assembly. Apply the loads to the structure and Probe the forces going through each Fixed Joint. Make sure you have a coordinate system that has one axis aligned with the screw axis. After you obtain the three forces on the Fixed Joint, use vector addition to combine the two in-plane forces as the total shear force. Compare this shear force with the allowable shear force for the size and material selected for that screw.