Spotfire Ideas Portal
OVER expressions are extremely powerful since they can achieve the same slicing and dicing of data which you can achieve using pivot transformations but in are more interactive way operating on subsets of data tables.
At the same time most users who can configure a pivot transformation with its GUI fail to get the OVER expressions right as it is just difficult to get your head around what are row identifiers, what are column identifiers etc.
That said, OVER expressions are rarely used in fear of making a mistake and it would be super helpful to a more guided interface to make use of them in expressions.