Smart Lists can act as a virtual dimension in your cube that may represent data points and they can be leveraged to pivot data points to actual dimension members while you are pushing data from source to target. Here is one example, suppose you have got this data point in your source.

You can define the Smart List for a dimension from Target cube, in this example RU (Reporting Unit) dimension does not exist in the source, only in target.

You can select Smart List as your source when mapping Reporting Unit dimension during data map definition as follows.

Once you execute the data push, you can see data transposed into physical dimension members.

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