Of course there is. If you need to pay for a node, showing ads may be the only way to finance it. And I also can have a node just for showing ads to a network.

Of course there is. If you need to pay for a node, showing ads may be the only way to finance it. And I also can have a node just for showing ads to a network. Imagine Facebook as the network and the members as peers. There are many peers who just advertise something.