They can be a life saver or a curse depending on how you use them. They do cost you money however if you let them get out of control and don't manage them effectively; you could find yourself in trouble and in debt.
Self control and understanding that you are responsible for the debt that you incur is the first thing that you need to be aware of and that you will have to repay any money owing. The effect this has on your long term goals could be astonishing. It affects your credit rating and your credit rating has an effect on your lifestyle. It has an impact on your eligibility to get a loan to purchase a house or a car or any other major item. Store cards also show up on this report so if you think you can move to another location and start again, you need to know that that isn't always the case and you may have to face the music at some later stage in your life.
On the other side of having a credit card, it can get through a rough financial patch and tide you over until the finances improve. It can get you that bargain now and as long you are aware of what you can afford to pay, it can be a lifeline. It is good to have a credit card when you don't want to be carrying cash or when you are traveling overseas.
When applying for a card, shop around as there are all sorts of benefits that you could get such as low or no interest for a period of time, loyalty rewards and free travel insurance etc. Do the groundwork and find one that suits your needs. Make it work for you because it your money that you are spending.