Originally Posted by tomgoodman

I flew 727 S/O with a "dual pool" slot as DC-9 F/O. They would only call you for a dual pool assignment if they ran out of reserves, because then they had to pay you the monthly guarantee on the higher equipment. That meant you were rarely used, and only semi-proficient -- a questionable situation if both pilots were "dual pools".
Eventually, they dropped the program in favor of "green slips" as a safer way to handle reserve shortages.