1) creditcard is good for your credit if you paid them on time
2) creditcard is bad for your credit at the time you apply it
3) creditcard is bad when you apply for a mortgage and it becomes a default liability expense
Note:
1) If you paid your credit card on time everytime for consecutive 6 months period. credit card company will start give you a positive rating. And then you can buildup your rating that way. Also, part of the rating is rate you HOW MANY TIME YOU USE THE CARD, not how much you use the card.
2)Why creditcard is bad for your credit at the time you apply it?
It is because everytime you apply a creditcard, the company will pull/request your credit history to review and make decision. Credit history is made that way that if a company request it, your credit rating will drop a little. So, apply only when you absolutely needed.
3) Some bank will see a credit card as a default liability on your daily expense even thou you say you will never use. For example, when you said you live with your parent and paid no rent when applying a credit. Too bad, they will automatically put down $600 as default rent and submit it~
hope it explains