The Inferno is a late game weapon thats focused on killing light armored enemies with raw damage rather then relying on napalm. Sacrificing attack speed will reduce the rate that napalm can be applied to the targets.
-Allows the flamethrower to kill light targets quicker and with less ammo
-Reduces attack speed which increases the time to apply napalm stacks which could reduce damage per second against anything thats not light.
-Reduces movespeed for kiting class.