Fan Clutch would be better for engine performance in respect to efficiency, so it is a good part to have even if you don't have AC.
On a mechanical fan Clutch it will have a temperature specification at which it activates. The clutch when it is cold(car off or on) it will not be activated, so it will spin freely, so that the engine gets no cooling. The fan clutch at the center it has a heating element, metal wire that when it gets hot to the specified rating, the fan clutch will activate, so then it will be very hard to not being able to turn (better way of explaining it, it tenses up). Now with engine on, the crank pulley is driving the belts and fan pulley therefore turning the fan. When I say you can't turn, I'm referring that you are in front of the engine bay trying to turn it by hand with engine off (Of course duh!). You could also, bench test a fan clutch with hair dryer, or heat gun. See manufacturer temp at which it activates.
Separate note: Rockauto has fallen off my shopping go to. They have gotten rid of many of my parts. Recently started to ask for lot more identification information to make a purchase. Along with no one to talk to on the phone to resolve concerns. you are emailing bots and AI.
