The units and scale you use are very important.
Modular meshes should be built to snap to a unit-based grid, and physics calculations depend on certain scales.
Fortunately, game editors usually have a scale setting you can use on import to convert from 3d modeler scale into proper game engine scale.
- Poll: What unit system do you model in?
- UDN: Unreal Units - what units and scale to use for scenes in Unreal Engine. (Gears of War: 2 units = 1 inch, Unreal Tournament: 1 unit = 2 cm)
- CryENGINE SDK: Measurement Reference - what units and scale to use for scenes in CryEngine. (Crysis: 1 unit = 1 meter)
- Unity: Import Settings for Meshes - what units and scale to use for scenes in Unity. (Unity physics: 1 unit = 1 meter)