All geometry in Detect3D and in:Flux is a collection of triangles. The conversion of complex surfaces into a set of triangles is called "tessellation." Very often, the default settings for which CAD programs export are not appropriate for quick analyses and will lead to overly detailed geometry.
In general, the smaller an object is the less important it becomes to the accuracy of the simulation. It is wasteful for computation time to use 500,000 triangles resolving nuts and bolts on flanges and other superfluous CAD pieces.
Spending time to reduce the number of triangles in the geometry will be time well-spent to significantly increase computation speeds. Note that even If you convert a CAD file using external software, you have control over how many triangles are created.
This section will go into how to properly use the triangle reduction capability used in Detect3D and in:Flux.