The main differences lie in the liquidity, and what you can use the money for once it is in the account. With an account at a brokerage, the use of your funds is directly tied to investing. You can only use the money for buying and selling stocks, funds, bonds, and other available securities. On the other hand, if you choose CMA as your account of choice, you typically also get a debit card and sometimes even checks. With such an account, you can effortlessly direct your funds elsewhere, make purchases, pay bills or withdraw your funds at the nearest ATM.