As to having utilization on the card, normal usage is enough to ensure that there is always a balance due on the card anyway. (If you spend money on the card regularly, the payment you send in August is for things you bought in July and by the time it posts, you have more August charges on the card, meaning the balance is only ever zero if you do a massive return or if you have a multi-week spending embargo hit at just the time the credit company pulls your report.)
Not sure what the mechanics are behind the scenes, but I keep an eye out for interest charges and I haven't seen any for years.
> meaning the balance is only ever zero if you do a massive return or if you have a multi-week spending embargo hit at just the time the credit company pulls your report.
I think I implemented the $10 policy because I wasn't using my cards very much at the time. Your system makes the most sense for anyone who uses their card regularly.
(The 90% is my Target Redcard with a $300 limit, pretty easy to max that puppy out... in fact its bad for my credit to even use, as the 90% utilization makes me look in trouble, but it can be hard to pass up 5% savings..)
Your bank may not want to increase the limit on a credit card you never use, but that's about it. If you want a high credit score, get the highest limit you can, always pay it off, keep it around for a long time, and never miss a payment for over a month. You also want multiple lenders (a single credit card won't, or multiple ones from the same bank won't cut it).