The differance is that its hard for a game map generator to generate exaxt worldmap as TR has.
TR is made specially for the purpouses of World Map, but users are free to start a cusom game, differant scenario or custom scenario.
The problem exists, that maps not designed for Total Realism need, may not have resources that exists in cutom games and on WorlMap, so features that require those resources will be unavailable and will require manual adding those with World Builder.
Other problem is that foreign scenarios may use building/units/resources/terrain types that are not supported by TR. In such examples you may expiriance crashes and other forms of noticing that this scenario is not compatibile with our mod.
How ever there is a chance that such resources/building/units/terrain types/improvements may simply not exist in our mod, leaving empty titles for resources, units/building/improvements will be not existing in game (if premade, they will dissapear in game). New terrain types are problem, as eigther they will crash game, or they will be showed with no graphics (pink color), or will be replaced by "default" existing terrain (ocean or grassland i think).