After a drive, I’ll switch the car off after parking up but sometimes if I turn the key pre-ignition, the fans will run for cooling I guess. I just leave them running until they stop (2 or so minutes) then pull the key out. Does it make any difference letting them run or not…

 

If the engines not running neither is your water pump, your cooled radiator water will be sat there not circulating.

 

It actually is that's the idea of the Subaru header tank. Convection takes over and the hot water rises from the turbo and is replaced by cooler water from the block.