mgs wrote Building the new table is a process which is done for the cube. Why should a customer want to build every possible combination?

Building every possible combination can be done any time. Building with actuals means it must be part of the ETL. And, the logic is more complex. For each record you have to get the combination and then do a lookup. If a match exists, grab the key. If no match is found, insert the record, atd then get the key.