I know most people use credit cards, but I've only ever used store bought game cards. I don't like that whole continuous billing they love to do to your credit card. Time cards allow me to set a strict limit on how much I spend on these games and not get carried away buying months of time, especially if my interest runs out.

Not to mention, lately I've only been playing f2p games so these are just a handy way of buying a points package for what I want or feel I should spend in their stores for any given period of time.