How to strike the right balance between accuracy and solve times has been a major consideration for analysts since the inception of FEA.
In an ideal world we would include all parts and mesh each thread and fillet to ensure we have captured every detail of the model accurately. However, experienced analysts know that even with the luxury of modern-day processors, for many applications this is still a pipe dream. In reality, we tend to use our engineering judgement to omit certain parts or features and reduce mesh densities to reach acceptable but compromised solutions.
Luckily for us, Abaqus has a couple of “have your cake and eat it” solutions to this perennial problem in the form of substructures and sub-modelling.