Overdrafts are only for short term borrowing cos banks can demand repayment in full any time, while loans or credit cards have a clear deadline. I’ve not tried getting the max amount, only enough to cover a month’s living cost.
Yes, it’s a very expensive way to borrow. My overdraft is for emergencies only and I only started using one at all after I was in hospital with sepsis for a few weeks and a credit card DD was refused because I hadn’t moved some funds into my account after an expensive purchase.
It harms your credit worthiness, too. I think due to the lack of repayment structures, some people think it’s an extension of their bank balance rather than a form of expensive short term borrowing.
I did think of reducing my arranged overdraft limit as I hardly ever dip in it, but as you’ve experienced, you never know when a misfortune could interrupt your credit facilities, so it’s always useful to have that safety cushion.