Identical parts can be a member of different assemblies. One may have a ventilation system that they wish to view select or highlight by various aspects of that system. A part of the overhead may be also in the wall assy but still both are part of the ventilation system. One may want to highlight everything w/ insulation attached, then I want to select everything in the overhead. Next I want to change the color of every component requiring sheetmetal. I would need to individually set up an extremely arduous amount of views and LOD's for any complicated space.
Folders within an assy only help a little as an item may in an overhead folder but when I need to quickly select by insulated materials to change a view or in the middle of a demsostration I don't have this option.