Ans: The viscosity of the fluid is directly proportional to the pumping power needed to transport the fluid from one place to another.
The pumping power is what decides the required capacity of the prime mover (generator, diesel engine) or electricity taken from the state electricity service.
There is a cost associated with every unit of power that is needed to be provided for pumping.
Hence more viscosity means more friction and more energy drawn from prime movers.
more viscosity = more friction = more power = more operating cost
This can be explained by using the example of cooling systems in large electronic equipment. Air cooling systems(blowers) draw lesser power (less viscosity of air) compared to the power requirement of the oil pumps in liquid cooling systems because of the more viscosity of coolant oils.