There are scenarios when Transformation End Routine is a good fit. In my blog will demonstrate how to simplify Transfer Rules by means of:
In my case I load PO GR data and lookup multiple characteristic values from PO Item level. Instead of repetitive coding similar lookup / mapping for each characteristic in individual Transfer Rule I did once in End Routine. It saved me not only coding efforts, but also increased performance by reducing a number of lookups.
During PO GR data load I calculate Delivery Duration based on Due Date, Delivery Duration based on GR data and over / under variances of two durations. I did not like the idea to repeat durations calculation logic in variance transformation rules. Instead I used results of duration calculations in end routine to calculate variances.