I think Compond Dai is awesome,because The simple answer is that by designing cTokens as ERC20 tokens, Compound has opened up a whole new world of functionality and liquidity. All the assets that used to stay locked away in Compound are now free to move about the ecosystem, ready to be utilized for other purposes.
You can transfer, trade, or send cTokens to cold storage, just like any other token on Ethereum. In fact, you can even integrate them into other protocols. That is, any protocol where you can lock tokens could choose to accept any cToken. This would allow you to earn interest on top of the benefits the protocol already gives you.