Coin Dance filters duplicate nodes by address, so individuals running more than one node at a given address are only counted once.
This helps give (although does not guarantee) a better picture of node decentralization/ownership, as it is understood that a single party running multiple nodes at a centralized location doesn't provide any additional value to the network.
In addition to this, Coin Dance also ignores non-listening nodes which have a maximum of only eight outbound peers.