The logic of property sets in #IFC is that they are added as a package to a certain class or type. If you add them to a high level class (like IfcElement) all derived classes inherit the possibility to use this pset.
While throwing all properties into one pset makes some tasks easier (checking in Solibri for example) the property management gets really complicated. Don’t add psets with the same name but different contents to different classes.
Think of property sets as “features” of your element.
Is it made of concrete? Add Pset_ConcreteElementGeneral.
Is it precast? Add Pset_PrecastConcreteElementGeneral.
These are like modules. So when you generate your own property sets please use the same system.
If properties only apply to a certain predefined type of a class like IfcFurniture.CHAIR then use corresponding Pset_FurnitureTypeChair; for common properties for the overall furniture class use Pset_FurnitureTypeCommon.
Three things to keep in mind here:
1) yes, it is confusing that it is not called Pset_FurnitureCommon (like Pset_WallCommon).
2) don’t confuse Pset_FurnitureTypeCommon with IfcFurnitureType. The Pset can define occurrences and types, respectively. Also quite confusing at the beginning.
3) don’t use “Pset_” as a prefix unless you use the definition from the IFC schema. It is a not so well documented convention. You will make your BIM managers/coordinators very happy!