For better visualization

[Fenice_1965]

[QUOTE][We don't want to control ground objects, we just want them there doing basic things. If they are not there then you do not have the realism required./QUOTE]
+1
an engine with different categories of objects is much more flexible in terms of resources management.
If some objects need only to be static targets we do not mind that they "have a brain".
Usually a mission has combinations of different AI objects (stationary, moving, shotting ......). This way you can setup complex game areas with lot of objects, lot of targets, lot of activities to do for the player.