There are advantages and disadvantages of using either options, however in my opinion the advantages of permanent work tables outweigh the advantages of # tables for ETL but # tables win for TP systems

• permanent work tables are available for debugging
• permanent tables can be conditionally created – whereas temporary tables can’t

however,

• # tables are automatically cleaned up whereas you have to manually either recreate or truncate work tables
• # tables always live in tempdb (although you can also create permanent work tables there as well)
• # tables are unique to the session so never any risk of contention