If you do 20 sets, you are likely trading too much weight for amount of sets, this does not help the principle of progressive overload.
After 12 hard sets total your next sets will likely be below the treshold intensity to stimulate additional growth.
So yes, do as low sets as possible AND do as much sets possible while being able to retain sufficient intensity.
Thos guys with gargantuan chests , training Yates style, likely have nearly all white fibre pec muscle wich responds well to low reps / sets and CAN only be taxed for several short hard sets because white fibres have no capillaries to grow, but if you like me, have a more mixed fibre makeup, you should at least do some additional work for the type 2b intermediate fibres.