KB4374: Are transformation tables needed to create transformation attributes/metrics in MicroStrategy?

No.
Transformation tables can certainly be used if they exist in the database.
Alternatively, a transformation based on expression can be created.
 
To create a 'Last Year' transformation, for example, follow the steps below:

• Create a new attribute by selecting File > New > Transformation. The following window appears:
  

• Click on 'Add' and select the attribute to which the transformation will apply, such as 'Year.'
  

• Double-click on 'Year_Id' to move it to the Form expression window. Add a '-1' using the operators in that section.
  

• Click on 'OK' once to close this window. Select 'Save and Close.'

A transformation for 'Last Year' now exists, which can be used to create a 'Last Year - This Year' sales report.
KB4374