Spin-off from the other thread. It's embarrassing to admit but someone else said it and there are no stupid questions, so here we go.

I know I have an overdraft of £200 on my standard Barclays current account. I've been very lucky that in general I've never had to go into it (maybe a few times by a few quid a day or two before payday). It used to be interest free when I was a student but isn't now. What kind of dollar could I be wasting on this thing? Is there any benefit in making use of it (good for credit or summat?) Or is it best to see it as safety net and avoid at all costs, and keep thinking zero is zero.