Here is my understanding from an implementation perspective, let me know if that makes sense.
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It’s not exactly easy to rebuild true multilayered element geometry using IfcMaterialLayerSet. That requires a full-blown modeling system and looks out of scope for RV, though that makes complete sense for DTV. For one thing, receiving app must be aware of multilayered wall joins which is a world of its own.
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On the other hand, IfcMaterialConstituentSet+IfcShapeAspects (i.e. generalization of layers) mechanism with separate geometric items for each layer is much more straightforward for receiving applications to process and use for reference purposes. Exporting software is sorta forced to bake complex implicit layered geometry into explicit (i.e. reference) when using RV.
I vaguely recall reading @TLiebich explanation somewhere but can’t find it.
