Mind, it's not necessary to add it in order to make / setup ads. It just makes it a little more convenient to access and stuff.
Also, it bothers me that there's no way for me to remove my credit card information, even though the transaction for my recent advertising request has already been completed. This is a problem, 'cause if anyone get into my account, they could potentially advertise random stuff and cost me quite a bit... (I think there's a daily spending limit, but I also think it's somewhere in the $250s. Which is a lot of money per day.)