Exchanges are brokers. They hold your crypto in a centralized (but decentralized?) location and you buy and sell coins on that platform. A wallet (Loopring or otherwise) is a storage place that you and only you have access to. You can't sell directly from a wallet, most of them anyway, so in order to cash out you need to transfer from wallet to exchange which will incur a gas fee. Transferring from the exchange to a wallet will also incur a gas fee. So if you are planning on holding any crypto long term you should have a wallet. If you are holding for a short term then just keep it on exchange where you can buy and sell directly without extra transfer fees. Wallet is more secure, exchange is more convenient.