I learned from my own experiences and others that credit cards are scams. If you have the money or access to it then you'll never need credit. If you want to spend money you don't have and might never have, then credit is available, with lots and lots of interest so that if you lose your job or employment based income stream you are stuck.
The only thing I use credit for now is when I need to pay for something faster than I can transfer money to a bank and they wont take cash or anything else. Credit is a last resort and choose to pay entire bills off a week or two after making them or sometimes even in the same day. Basically if it's money I already have in some form then I use credit.
RE: Why You should AVOID A Discover Miles Credit Card