Cash settlements take several days. So while that is correct, a margin account let's you use funds from the sale of a stock immediately instead of waiting for

Cash settlements take several days. So while that is correct, a margin account let's you use funds from the sale of a stock immediately instead of waiting for the settlement to occur. You aren't taking out any margin (with interest) in this case, just using the funds you already have (but haven't settled). Otherwise a cash account limits how much you can trade very quickly since you are waiting on trades to settle.