Last time I changed my overdraft amount, the teller told me that I actually stood a better chance if I wasn't doing as well financially. She confided that if I was making a good extra income and stayed out of the overdraft, it may not get approved. If I did a bit worse financially, it looked like I "needed" it more (her words). The implication being they would make more money off me, so I was more likely to get it, as long as I wasn't too big a risk.