Row level calculations (calculations that are performed for every row returned from the data source) may be used as dimensions.
[ calculations performed as an aggregate for whatever level of detail is present in your view -- e.g. SUM(Sales) ]
and table calculations
[ calculations performed on the table of data returned by the initial query -- e.g. WINDOW_SUM(SUM(Sales)) ]
are not able to be used as dimensions. They cannot slice or partition your data as they are defined by what is slicing or partitioning the data already.
Ah. Of course, thank you for the prompt reply!