Quote from rallymode:
Just a little warning for those of you who intend to put 100% of their cash on hand into an EFP in search of a higher yield. If the stock you picked takes off your cash account will go debit and will start generating debit interest due to the SSF being settled to cash daily. Your cash account will go negative by the amount your stock value has gone up.
To illustrate this with an example: A 100% move up in the stock will cause you to pay debit interest on your entire account, assuming you put 100% of your cash into an EFP. In which case, you end up paying ib the spread between the yield you locked with the EFP and their debit rate. On the flip side, your cash goes up as the stock tanks.
Just something to keep in mind.