Let me explain it with examples.
On Bitcoin protocol, for example, you have Counterparty. As it uses embedded consensus, every XCP address is linked to a Bitcoin address. So if you hold bitcoins on that address, you can also hold XCP on that address and even more tokens (such as Storj).
Is something like that possible on Ethereum ?
I mean, can you hold other tokens than Ethers on your address ?
Can you even hold coins from other blockchains on an Ethereum address (for example, Bitcoin, Litecoin, etc.) ?