Quite a bit has been said about the subject... some of it being true, some of it not being so true. To help "clear the air" about it...
The best practice for solids modeling in MicroStation is to keep it simple. If you consider a 3D model in a V8 DGN file to be a "universe", keep your model at the center of that "universe" (i.e. TRUE 0,0,0). When you do that, your results will be predictable and precise. If you want to create a 3D solids model that will be used as part of an "assembly" with other models, then take advantage of MicroStation's global origin and reference using the Coincident World attachment method. You should definitely NOT create models that are far away from the center of the "universe" and use the global origin to try to make the model look like it is at the center of the "universe".
So remember, "Stay close to 0,0,0, my friends".
We are starting to create 3D solids in MicroStation, OpenPlant Modeler, and AECOsim for our facilities. These use CA State Plane coordinates. Our file resolution is 12000 units per FOOT, and we accept the SWA working area that is calculated. Considering that our XY coordinates are in the range of 6200000, 1800000, should physically move the graphic elements closer to the center of the design cube and and reset the GO? The largest extent of any of our 3D models is 5 miles x 5 miles.