This sounds like snake oil, the fan clutch is not adjustable but can go bad. When they go bad the fan gets stuck on all the time. If this is the case there should be no harm to the truck, it is just inneficient. Even if you were to replace the fan clutch, the cost should be minimal.
Yes you may need to spend the money because there may be several steps involved in replacing the clutch. There may be several hours involved and you may also have to buy a new clutch as a whole.