In the advanced physics article, it is said :
Note that you should share collision shapes in general and that j3o files loaded from file do that as well when instantiated twice so this is something to consider.
Does this mean that meshes aren’t loaded twice from an imported model or that j3o loaded files will generate collision shapes once?
Well, that sentence is using very bad grammar so it’s hard to parse what was actually meant.
If you load “car.j3o” form a file five times then all five instances of that will be sharing the same mesh, collision shape, etc…
If you load some other thing from a j3o then it will not share collision shapes with car.j3o objects.