This may not be a genealogy issue but it certainly is important for security and peace of mind.
One of the things I detest about many web sites is that when you sign up for a subscription and pay with a credit card, the site automatically renews your subscription when it expires. Some web sites will automatically renew without even the courtesy of notifying you in advance. They keep on billing, and you cannot easily shut down the offending vendor.
Of course, you could cancel the credit card itself, but that usually isn’t convenient.
Another risk, although rare, is that someone might obtain your credit card number surreptitiously and make illegal charges against it. While all online charges are insured by the credit card companies so that you will never lose any money, going through the process of filing a claim and getting your money back can be inconvenient, at best. I think it is better to stop such an illegal transaction BEFORE it occurs.
Luckily, these problems are easily prevented if you take appropriate steps in advance.