About shared dimensions
When a dimension is shared, all members and member sets that are contained in the model site are shared with all model subsites below the model site in which they are created. Dimensions that are not shared are only available to the model site in which they were created. You cannot share some parts of a dimension with model subsites but keep other parts of the dimension private. If you create additional members for a shared dimension in a model subsite, those members will not be visible to the ancestor model sites. However, they will be visible to descendants of the model subsite. Member sets that are shared from a model site cannot be extended in model subsites.
An example of a frequently shared dimension is the Product dimension. The Product dimension is created in the root model site and is shared with all model subsites. This means that sales for all types of products can be analyzed for the whole corporation at the root model site. It also means that products that are associated with each business unit can be analyzed in the model subsites.