cash = debit card
if you dont have money you cant make a purchase
if you have 3.47 in your savings and go to get gas with your card, you will get 3.47 in gas
if i go into the bank and deposit 200.00 into my debit , walk out, walk back in and ask for 200 dollars, its the same as me buying something thats 197.30 on my debit, except i didnt go to the atm physically and get subcharged.
i dont think debit cards effect your credit..they might, but i doubt that
i only use my card for gas and online purchases, outside of that i use cash and i go to my bank so i dont get subcharged and probably save a good 100.00 annually by doing so