The ability to move heat is caused by a heat gradient. The larger the difference in temprature between 2 objects the faster heat moves to the cooler one. If the air inside your case is significantly above the ambient air temp outside the case and you are concerned about your proc temp (think its too high or just want it lower) then it would be better to add case ventilation to provide a greater temp difference inside the case and improve the cooling of the proc. This is when you add a case fan. HTH