I would hardly consider an e-fan useless. They can free up quite a bit of room in front of the engine making some work much easier, which I find to be a huge benefit. When done right, they have absolutely no affect on the engine when you are at speed as they are not on... a mechanical fan however is always there. The fan itself may not be spinning but you do still have the clutch, which is excess weight that can be removed from the engine (yes, I know it is not much weight but any weight lost is... weight lost, and rotational weight too. You may not see a power increase but it may make your engine a bit more responsive i.e. think lightened flywheels and crank pulleys).
But anyway... I find the biggest benefit is the increase in room in the engine bay, that is always a great thing to have. Also, getting rid of that nasty mechanical fan sound is a nice bonus as well.