One thing I'd further like to add is, don't go overboard by dividing a model into too many submodels either. In the end, more models have a little bit more overhead in terms of system memory, matrix computations and device state changes (swapping a material, setting renderflags), so you have to balance it out a little. The best rule of thumb probably is to stay away from large models with big dimensions that will always be in view when they are not cut into pieces. In interiors you can probably get the best improvements, for instance:
- don't use one big model for the hull because then it will always need to be drawn no matter where you look.
- Don't combine two desks in an interior that are spaced apart 40 meters...
- etc.
For the very same reason, ship hulls (even though big dimension), are usually one big model, because you are likely to see it completely anyway (you are not supposed to be only 50 meters away from it right?), so breaking it apart doesn't give you a performance boost, on the contrary...
Confusing?
