Surely that's only when it's set up. After that, there may not be enough money to pay a DD, standing order, or regular Bacs transfer. It may sound perverse, but it's even /more/ likely when you pay many bills by DD. That's especially true when, for example, a utility company increases the amount without giving proper warning (as they should do, but...). And what happens if the company - accidently of course - moves the decimal point so they get 10x the amount they were supposed to, and it drains your account and/or puts you into an overdraft state? Of course they have to repay you according to the DD guarantee, but it could leave you trying to sort out a payment mess if other DDs aren't met when requested.