I am going by how long the procedure or function takes to run, with resources available to the server being basically the same for the 'derived table' run and the 'table variable or temp table' run.

Replacing derived table(s) with table variables or temp tables has cured lengthy run time problems for me. These problems occurr when the tables accessed have large numbers of records.

I do add primary keys and / or indexes to the table variable or temp table when possible. This may be a significant part of the performance advantage I have observed.