If there is little or no airflow over the brakes then releasing the park brake can, in fact, reduce the rate of cooling, as the gap between the discs is tiny and heat is simply radiated across the gap from disc to pad (and v.v)
By leaving the park brake set the heat can be transfered and radiated (away) through the whole assembly.
Don't agree, small gap it may be, but even without a breeze it will still set up a convection current, same way the radiator / heater bolted to your wall does, and for that matter the same reason why said heating device has fins and isn't just one big lump of metal, greater dissipation / transfer of heat.
I would advise as seldomfixit suggests, one never measures the amount of brake wear with brakes off, unless you are minutes from finishing your shift and feel the next shift should change the worn brake unit
