ehhhh.....I don't know who told you that, but they are dead wrong. A fan clutch can be a power advantage over a solid fan by allowing the clutch to coast the fan at road speed if it's a thermostatic fan. The thermostat cools down at highway speed and unlocks the clutch allowing the clutch to spin and not drive the fan, which reduces drag on the engine drastically. This is the whole reason Mopar Performance offered their viscous fan package.
Conversely, as the temperature increases, the thermostat changes position making the clutch lock up more and drive the fan harder. This is why they sound like an airplane on a hot day. So yes, it most certainly is a cooling, MPG AND power thing. The MP viscous fan package is one of the best things you can run if you have the room and if you can find one.
