Why should I get a credit card?

Only real reason is that it can be useful tor establishing a credit history, and if you put a decent amount on it the miles can be nice.

You should get one early so you can start building credit (will be useful if you decide to buy a car/house and get a loan). Just make sure you don't abuse the card.

you also get 1-2% cash back or other rewards with a lot of cards. meaning that if you pay off your balance on time, it's like getting 1-2% back on everything you buy.

1. Working capital benefits. You can basically float purchases a month allowing you to manage cash flow and push out capital outflows.
2. Without it, you are throwing away 1-2% in cash back, miles, etc...
3. Credit cards allow protection (returns, warrantee, travel protection, Identity protection) that debit doesn't grant.
4. Building credit is pretty much essential in today's world.
5. Premium cards give you access to programs you can't have without them. i.e. Priority Pass, Consierge services, Amex Travel Benefits, Preferred Offers)

Definitely get a cash back card. The Amex Blue Cash card pays 1.25% back on all purchases and 5% back at gas station, grocery store and drug store purchases once you spend over $6500 on the card. There are others as well.

It's also good to have a credit card for big purchases or emergencies. Most debit cards have a $1000 daily limit on them.

It's a necessary evil, I'm going to get Barclay's with US Air so I can rack up some miles and maintain my silver status.