Well, I hope they don't do what Amazon does. Amazon doesn't allow you to bypass a gift card balance for purchases. I've had times where I wanted to buy an electronic device with only my credit card (for free extended warranty) and Amazon wanted to apply the remaining balance from my credits and gift cards before using the credit card. CS calls revealed it was policy and too bad. They suggested I use up my balances and then make a credit card purchase. Totally unsatisfactory.
Bottom line, I rarely shop at Amazon anymore and avoid their GCs; unless I can get one for half off. In which case, I spend it right away on classical music.