We always use our room key for all our purchases including all our gratuities. It is simpler for us to only have to worry about using the one card and we find it is easier to check over our bill at the end of our stay rather than waiting a month later and checking our credit card statement and trying to remember what each charge was for.
Our kids are too young to carry their own cards around, so we don’t have to worry about the charging right now. But, when my sister and I were younger, our parents just gave us the card without charging privleges.
As we got older and started to go off on our own a bit more, we were given cards for charging, but only for “emergencies”. It was a good learning tool for us to learn the responsibility of spending and safer for us than carrying cash around.