[Kintsukuroi.]

I have 4 credit cards in my wallet. Three are linked to my parents (one is for only for gas and another is for anything other than gas) and we have on the we use only if we are in the United States/travelling (and for concerts presales lol) and then I have my own that is used a few times a month in order to build up my credit score, usually from stuff my parents have me buy for them.
I've always been taught that don't buy anything unless you have the money to pay it off in your account and I've had my card for a few years in my own name (not linked to my parents) in order to build up my credit score which is important. My mum pays them off as soon we receive the bill (that's what we were told by our various cards is best).
When my parents buy new cars, they charges them in full on the credit card and then pays the card off after so they gets the points. My dad doesn't believe in leasing vehicles so he uses the card and then pays it in cash (and gets less of a look if he was to pay in actual cash/transfer). That way our cards don't have a ballence owning after the month is over and we get points/cash back as well which is an added benefit.

I've been raised to pretty much treat it like a debit card and that's what we do and avoid interest. I think they're important providing you are smart with it and don't get into debt.