The general workflow is incredibly streamlined because the slow speeds of blockchains don’t impede trading, and everything occurs in a single entity’s system. Cryptocurrencies are easier to buy and sell, and you have more tools available to you.
This does come at the cost of independence: you need to trust the exchange with your money. As a result, you expose yourself to some counterparty risk. What if the team runs off with your hard-earned BTC? What if a hacker cripples the system and drains the funds?
For many users, this is an acceptable level of risk. They simply stick to reputable exchanges with strong track records and precautions that mitigate data breaches.