Just curious here...

My new baby, a magnificent, adorable, comfortable Merlin CR 3/25, comes with elegant Fulcrum Racing 7 wheels, which certainly look fast with those neat red hubs, and seem to perform just fine for the 200+ miles I've done so far. But they have that clicky Campy whirr when you freewheel, which you don't get on Shimano wheels at all.

But why is it there? Does the friction of the whirr slow the wheel down at all? Is it a message to me that I should be pedalling all the time? Or is it just because?